Undercoating or sealant?

[Denise K]

When I replaced (OK, I didn't replace it, a carpenter did) the floor on the back of the MKP (you can see photos of it on RolyPoly Cottage )
the masonite-like layer at the bottom was removed. Though I had requested it be replaced with a new layer, the carpenter skipped this part. Now the underside is the treated plywood.
My question here is, should I apply a coat or two of Thompson's Water seal to the exposed areas? Is there another sealant to help protect/prolong the life of the plywood belly?
The MKP is my only experience with FGRV's so I don't know how everyone's else's egg bellys are protected.
Is this a stupid idea on my part?

[Pete Dumbleton]

If it's treated plywood, then you really don't need any kind of sealant because treated wood is quite resistant to rot -- However, it might be a good idea just to keep the wood from absorbing water vapor and weight.

Had you thought of it in time, it would have been a good idea to seal the UPPER part of the wood to prevent the gasses from the treatment from being in the inside air -- Be sure to air it out often before you use it, esp in the first couple of years.

BTW, if I were rebuilding an egg floor, I would likely use treated wood for the durability, altho it is heavier than untreated wood -- Likely, I would let it thoroughly season and then seal it on top (or maybe both sides) before installing.

[Frederick L. Simson]

I don't know how everyone's else's egg bellys are protected.

The bottom of my Fiber Stream's floor is covered with a thin guage sheet aluminum.
All seams, penetrations (gas lines & conduit), fasteners, and the joint with the fiberglass shell are thoroughly caulked.

[Cam A]

I don't know how everyone's else's egg bellys are protected.

Some trailers have a continuous fibreglass bottom, with the wood floor glassed into it. Although it would be messy to do from the bottom, you could apply epoxy to seal the wood from below. To really stabilize the wood moisture, you need to encapsulate it by sealing the wood on both sides with epoxy. I am not sure how epoxy likes treated plywood. If it was my trailer, I would prefer having something to protect the plywood.

[jack maloney]

Don't know that I'd want to completely seal the bottom of an egg. Damaging water usually comes from above, not below, and a totally sealed bottom will hold in any moisture that leaks in from windows or roof. The plywood floor of my UHaul is sealed with epoxy/FG - but there are several openings where any water coming in will drain out.

[Roger H]

Some trailers have a continuous fibreglass bottom, with the wood floor glassed into it. Although it would be messy to do from the bottom, you could apply epoxy to seal the wood from below. To really stabilize the wood moisture, you need to encapsulate it by sealing the wood on both sides with epoxy. I am not sure how epoxy likes treated plywood. If it was my trailer, I would prefer having something to protect the plywood.

Cam, actually the enclosed floors can be a bigger problem than the exposed floors. As Pete pointed out, most floor rot comes from pooling from above, or from running in somewhere. Plywood floors don't suffer rot damage from the bottom up, it's always from the top down. Even if you decided to completely undercoat your trailer, you'll never get plywood perfectly sealed, especially after the trailer is built because you can't get to the edges where the plies are exposed. I think that actually you're much better off allowing the wood to 'breath' naturally, or at least provide places for the water to run out and for the wood to dry.

I think that a spray-on or roll-on application of Thompson's or something similar certainly wouldn't do any harm, but I don't think it'd really do any good either.

Roger