Dear Dave,
What is the best way to protect and insulate the underbelly of an RV? I have seen where the manufacturer will cover the entire underbelly with a thin corrugated plastic. I have also seen where the manufacturer simply sprays insulation on the entire underbelly, leaving the underside exposed, assuring access to vital components, valves, tubing and wiring. Which method do you think is better? Thanks. —James, 2023 Escape 5.0TA 5th wheel
Dear James,
There are pros and cons with both methods. I believe the decision comes down to the price point when RV manufacturers decide what method they’ll use.
Spray foam insulation
The spray foam expands and covers the entire underbelly. Although you can get to valves and tubing, as you suggested, it completely covers wiring, connections, and other components and makes them almost impossible to get at. It does provide good insulation and is cheaper to apply. However, it gets very dirty going down the road and is not easy to clean. Then again, who cleans the underside of their rig on a regular basis?
Corrugated lining
The corrugated lining does a better job, in my opinion, of covering the components and protecting them. However, it does not provide much insulation other than the airspace between the underside of the floor and the lining. And, as you stated, it covers all the valves, tubing, and wiring underneath.
I have worked on several RVs with the corrugated lining and cut a square in the corrugated material at the point of service required, trying to make the cut at a cross member. Then I applied a larger piece of the same material over the opening that was then painted black to match, and nobody knew the difference.
It does take more labor to install the original corrugated lining, which means more labor dollars and thus the higher price point. I do think the corrugated underbelly is good when camping in colder weather as it helps keep the wind from blowing on plumbing and other components. I have seen many units that had the corrugated underbelly and spray foam at all the opening where pump valves and low point drains protrude out.
Combination of spray insulation and corrugated material
Maybe a combination of spray insulation on the corrugated material would provide superior insulation and protection with some access by cutting out the service area. However, that would be double labor and expense, and I doubt we will see that in models. The choice all depends on the type of camping you are going to be doing and the price you are willing to pay.
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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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Thank you, Dave! 🙂 I find it interesting that insulating the underside of an RV is cheaper than applying corrugated plastic. I understand now why; because the labor time is greater. It seems as though a plastic cover with insulation on one side would be better than either, but certainly even more costly in material and labor. Thanks again and safe travels, Dave! 🙂
We have a plastic bottom liner rather than spray foam insulation. Our ‘4 season’ depends on parasitic heat from the propane furnace ducts to keep water lines from freezing. There are times we could reduce our heating costs using electric, but at the risk of frozen water lines.
Dave
First good article you provide good sound advice.
The covered underbelly in my opinion really does help with the heating and dust migration. I understand the cost savings with that said the savings applies to all the work under the floor. I pulled all my coroplast and was shocked at the mess, wires run every which way not tied up, heating ducts many feet longer then needed or smashed (if its hidden behind coroplast who cares). It took me three days to straighten and secure the wiring, cut the ducting to proper length and add dampers at the plenum.