This is the crux of every decision an RV owner has to make, trailers or motorhomes, but especially trailers.
How much weight can I add, and where? In the case of trailers, where you put weight will and can affect tow ability, fuel economy and stability.
Your floor was never intented to be as strong as the floor in your home. It was meant to be light but strong enough floor to meet the needs of users. Adding epoxy to the floor on one side only will not add any strength at all. If anything it will add instability to the floor by encapsulating any moisture that enters the floor and possibly cause the floor to warp and heave as one side will expand and contract at a different rate than the other.
If you wish to put another flooring substrate on top I would consider a laminate or engineered hardwood flooring with cork backer as solid wood expands and contracts far too much for RV's. You couldn't glue down a hardwood floor anyway as it would eventually break the glue bond and start heaving. I wouldn't glue the flooring down as it would be easier to replace or repair if it's floating. I used a Torly's Everest Maple engineered flooring myself with 4 1/2 wide boards by 60+" and 36" long. You can even get boards 6 1/2" wide by 72+" long which would add strength. I however have a Classic motorhome so towing doesn't concern me, but weight did.
Just remember to try and think RV, not what you would do in your home. Two very different animals.