I had read one thread about a M109 camper conversion and that OP mentioned a couple times the metal cover or liner or something like that on the bottom of the box. This had led me to believe that there was a sheet metal cover over the underside of the box that enclosed the ribs/joists (Whatever you want to call them) and of course closed in the bottom side of the floor.
Is this not the case? In looking at the pictures on this thread it sure looks like there is no cover/liner closing off the bottom.
Just wondering for clarification.
Assuming there is no metal covering, I think the plan to undercoat it after the wood seasons/dries some is very sound. I would look into one of the commercial bed liner products. That stuff is all but nuclear bomb proof. They do make do it yourself kits but putting it on the bottom and getting 100% seal/coverage could take a very long time and would be pretty difficult to be sure you have absolutely no gaps. On the inside to protect against something like leaking or burst plumbing the do it yourself stuff would be real easy if you did it before you installed anything and the floor was still bare. Bring it up an inch or two onto the wall and you have a completely waterproof tub over your floor. As you make holes in the floor for plumbing and so forth you can reseal them with some more of the coating and be good to go till your at least 102...
I only mention this because in all my years water has caused me more problems than just about anything else. Broken/leaking pipes, leaks in the roof, shower enclosures that do not seal 100%... Home, truck, RV, storage buildings, steel conex boxes... they all leak sooner or later and when they do it is never good. So now I go way nuts overboard to protect against the damage and to try my best to prevent it from leaking in the first place.
Stage 1 is to try to seal up the outside as best that can be done. Stage 2 is to assume it is going to get wet and build it/protect it so that when it does get wet it can stay that way for months (if undetected) without causing any harm.
92? My grandmother lived to 106 and was sharp as a tack to the last day. Not sure I want to be replacing flooring at 92....lol....
(Of course at that point I just might not care anymore..... Sigh..)