How to Insulate an RV Underbelly

RVing is a whole universe in itself and off-roading enthusiasts can never get enough of this passion. For avid campers and Overlanding fanatics, an RV is like a home and no matter how harsh the weather is or how tough the terrains are, there’s no separating the two.

The RVs of today is much different from what we used to get a few decades ago and like the automobile industry, the RV industry has grown immensely. Modern RVs have sturdy build quality, have great utility, and come loaded with tons of features and amenities for luxurious camping and boondocking trips.

Although the RVs of today have all the latest equipment and features to offer you a 5-star experience, the weather might still take its toll on your trip and make it miserable for you. There are many options to keep your RV insulated and its environment cozy, but those might not be enough in harsh winters or when it’s down pouring.

You could use portable electric heaters, propane heating units, or solar-powered heating systems, these might be expensive to purchase and require a lot of maintenance to stay fit. There are cheaper, more reliable ways of insulating your RV’s underbelly and staying warm during winter trips.

If you’re wondering how to insulate an RV underbelly, this detailed guide is just the right piece for you and contains all the necessary information that you need for insulating an RV underbelly.

Tools Required to Insulate an RV Underbelly

Before we jump into the details of how to insulate an RV underbelly, it is important to know the basics of the procedure and know about the different tools required to perform this relatively tricky job. If you’re interested in knowing how to insulate an RV underbelly, you’d require the following tools:

A screwdriver.
Cutting tools, such as a router or a blade.
Measuring tape.
A flashlight or an electric lantern.
A marker.
Duct tape.

A Step by Step Guide to Insulating an RV Underbelly

Step by Step Guide
Once you’ve decided to insulate the underbelly of your RV and gathered all the tools, it’s time to get to work and get the job done. Here’s how you can optimally insulate the underbelly of your RV and enjoy those long winter trips, or fishing season without freezing.
Preparing the RV and Parking It Safely
Insulating the underbelly of your RV is going to take some time, so it is important that you prepare well for it. Park your RV at a suitable location, particularly where you could move under it easily. Then turn off all the valves and disconnect the batteries to avoid the holding tanks from flushing and working with wires easily.

Engage the parking brake, and put a nice rug under your RV so you can work comfortably. Gather all your tools and have your RV’s owner’s manual with you, in case you need to check something.
Inspect the Underbelly of Your RV
It is crucial to take a thorough look at your RV’s underbelly. This helps you get an idea of the frame and look for any damages that need repairing.

Mark the area that you need to insulate, and check and pinpoint the location of different pipes, hoses, wires, and connections underneath. Once you’ve inspected the underbelly of your RV, bring the insulating material and for your reference, you can take the pictures for proper connections and bolting purposes.
Measure the Size
If the owner’s manual is not clear about the dimensions of your RV’s underbelly, you’d have to take the measurements yourself. This is a much better way as it allows you to spend some time under the RV, and learn the location of important joints and other connections. It also helps you alter the design and pattern of the insulating material that you’ve planned to incorporate into your project.

Then use a measuring tape to note all the dimensions properly. For the length, you should take the measurement in full, and then in small patches for applying the insulating material, rather than putting one large chunk of insulator down there. If possible, also measure the width in full, and then in patches for ideal cutting and adaption of insulating material.
Detach the wires and Pipes
You’ve to make sure that the insulation is done perfectly and there are no loose ends anywhere. Leaving even a small patch or having the slightest deficiency would not do you any good on your winter trips.

For perfect insulation, remove all the wires and water pipes with connecting hoses from the underbelly of your RV. This allows you to adapt the insulating material perfectly and then put the wires and pipes back where they were. Make sure the battery is not connected and the valves of the holding tanks are tightened shut, for your own safety.
Installing the Insulation Material
If you’re looking for how to insulate an RV underbelly, this is the most important chunk of information that you should have. Before you go stripping the underbelly of your RV and putting on the insulator, you must know the few different kinds of insulating materials that are available on the market.

One of the easiest to manage and cheapest to get insulating materials is the solid foam sheet. Easily available and can be acquired in huge quantities. You simply have to cut it according to the measurements and attach it to the underbelly of your RV, either with double-sided adhesive tape or magic glue. The foam gives you complete freedom and you can either install it in patches or in one big section.

Another option is to use fiberglass as an insulating material. It is more durable than foam and is a versatile option, that you can use for insulating an RV underbelly. It is important to know that fiberglass is a tricky material and you’ve to be careful with handling and installing the fiberglass. Simply cut the fiberglass according to the measured size, and apply it to the underbelly using screws.

Another feasible option for insulating an RV underbelly is spray foam. It is one of the easiest options that you could choose and applying it is also very easy. You simply have to wear protective eyewear and other safety equipment and apply it to the underbelly by spraying it on the metal portion of the underbelly.
Adjustment and Finishing
After you’re done applying the insulating material to the underbelly of your RV, you ought to make it neat and finish it properly. This avoids any loose, hanging material that could cause a possible fire hazard or disrupt normal connections.

Look for any extra or bulging material, deficient parts, or rough surfaces anywhere. Using a finishing pad, properly trim and finish the surface of the insulating material that you just applied. This also helps you put back all the connections and wires properly.
Reattaching the Connections
Now that you’ve insulated the underbelly of your RV and finished the insulating material properly, put the wires, pipes, and connections back in their original place. You could also use this opportunity to insulate the water pipes and put a protective covering over electrical wires to protect them from environmental hazards and prevent water from freezing in winter.
Take a Test Drive
Once you’ve completed your project and are done insulating your RV, it’s time to take it out for a test drive and see if the insulation really works. Take your RV to a nearby lake for a few hours in the evening and compare the difference in temperature.

You could also take a BTU reader with you, and compare before and after readings to know if the underbelly of your RV is really insulated.

Insulating an RV Underbelly via Exterior Skirting

We have just learned how to insulate an RV underbelly and enjoy comfortable trips in freezing winters or when the mercury drops too low.

Although these insulating options are great and you won’t need to bring those loud and lousy heaters with you, it is good to have some extra insulation when you’ve parked your RV in the wilderness somewhere, or near a lake on your fishing trip.

Skirting is a cheap and feasible method of getting extra insulation. The best way is to get either the retractable cloth that folds down and acts as a barrier to wind or you could use plywood as well. If you’re planning to go for this option, remember that you’d lose a lot of space. The best option is to use the retractable fiber curtain that folds down and saves a lot of space inside.


Of all the materials that you could use to insulate the underbelly of your RV, fiberglass is the most durable one. It has high quality, superb strength, and provides adequate insulation in tough weather conditions.

Although slightly more expensive than the foam, it is more reliable and offers more dependable insulation than other cheaper options on the market.

You could synergize the effect of your underbelly insulating material by adding an extra layer of insulation to the floor of your RV’s interior. There’s no need to use any complex materials or get into complicated projects, simply take a thick rug that matches the size of your RV’s floor and have it laid down inside. Not only does it look good, but it also offers extra insulation and a cozy environment as well.

It is legal to add a layer of insulation to your RV’’s underbelly, as long as you don’t disconnect any wires and keep all the OEM connections intact. If your brake lights stop working or some electrical system gets messed up after insulation, you might not be allowed to take your RV on the road and get into trouble for that. It is ideal to get the insulation done by a professional, rather than doing the hit & trial yourself if you are not confident about it.

Though most manufacturers won’t have any problem with you getting the underbelly of your RV insulated, some companies might actually prohibit it and you could lose your warranty for doing it.

It is important that you check with your dealership or explore the owner’s manual before taking on this project, so you don’t get into any trouble later on.


RVing is a fun and adventurous activity, and with the right machine and proper preparation, you could have an experience of a lifetime out there. Though modern RVs come well equipped and built using high-quality materials, it is usually not enough to tackle the tough challenges presented by harsh weather, particularly freezing winters.

You keep the cold at bay and enjoy cozy evenings on a lakeside, it’s better than you get the underbelly of your RV coated. You could use foam, fiberglass, or spray foam for this purpose, and follow our step-by-step guide for perfect execution. To make sure that you’re not doing anything illegal or putting the warranty of your RV at risk, check with the authorities and your local dealership for clarity.

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Ever since I was a kid, I've been fascinated by travel. I inherited this passion from my parents. Since my college years and to this day, I have had a passion for traveling in a motorhome. I am here to share my experiences with you.

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