Hi Dave,
I have heard comments that my type of RV may be susceptible to exterior floor rot over time due to driving a lot in rainy weather. What is the best underbelly waterproofing that you recommend? Thank you. —Stephen, 2022 Venture Sonic Lite SL169VRK
Hi Stephen,
The first thing I would suggest is to visually inspect what you have there now. There are dozens of travel trailer manufacturers and they all use different materials and manufacturing methods. Some use a marine-grade plywood for the floor, which is moisture-resistant but more expensive.
When I was building my house, I got a very in-depth education on flooring options, and everyone had an opinion on what was the best. “Old school” contractors still like the traditional fir plywood. However, the “young bucks” stated that if it got wet before the framing could be closed up during the building process, the fir would split or separate, as it is in layers.
Plywood
Plywood gets its name from the layers of veneer or “plies” used to make it. However, there are several other types of flooring that are engineered in other methods but are generically referred to as “plywood.”
Oriented strand board aka chipboard
Oriented strand board (OSB), or “chipboard,” is manufactured using chips or slivers of various woods and pressed with epoxy under high pressure. The fibers or strands of grain of the wood chips are placed or “oriented” in a specific direction, typically crisscrossing each layer to give it more strength. It is a common product used in the floor and roof of many RVs.
Although OSB is water-resistant, the movement and vibration from over-the-road use can split the strands. OSB will swell more than typical plywood, so it does need to be protected.
Another disadvantage is the formaldehyde that can be released, although recent technology has greatly reduced the emissions.
Particle board
And then there is particle board, which I believe is the worst flooring option of all but have heard of some that will use it.
Underlayment
Most manufacturers will cover the underbelly of the floor with an underlayment such as this Tough Grade Polyethylene available on Amazon here.
It looks like this installed on a trailer:
Some manufacturers will cover the entire underbelly, frame and all, with a corrugated plastic sheet such as this.
If you have either one of these, the flooring material should be protected from moisture and damage. If not, you might want to install one of these materials on the underbelly. However, it might be difficult or next to impossible due to all the low point drains, axles, and other obstructions.
Spray-on undercoating
Another option would be to spray an undercoating on the bottom side such as a truck bedliner. A much easier option would be a spray-on undercoating such as the 3M product I have used. It can be found on Amazon here.
You might also enjoy these posts from Dave
- Where can I find someone to add an underbelly cover to my trailer?
- What is the best way to protect and insulate the underbelly of an RV?
- My trailer’s underbelly was full of water. Dealer said I overfilled the freshwater tank?
DAVE HAS ANSWERED MORE THAN 1,200 readers’ maintenance and repair questions. Read a directory here. There is so much to learn!
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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