Even though I am a gal... an old one now... I have replaced the floor boards in 5 trailers. Three of them were whole floors, the other two, were just a board or two. We (husband and self) had decided on pressure treated (we sold that trailer shortly afterwards), and, appatong (sp?). The appatong is the wood they use in the floorboards of over the road 18 wheeler trailers. It lasts in those trailers for many years, exposed to weather. The trailer we used the appatong in held up way better than the pressure treated floor I helped a girl friend replace. We had the appatong floored trailer for a long time after doing the floor, and, did have to replace the very back board many years after the original floor replacement, but, the trailer was parked out in the rain, and, was not cleaned out like it should have been. The other boards in the floor held up extremely well, looking not much different than when first replaced.

We bought the appatong from Edensaw Woods, who's main office is in Port Townsend Washington, but they have several warehouses in other states too. I'd bet it can be found many other places too, but it won't be a common one to locate.

We left spacings between the boards of about 3/8 to 1/2 inch so the liquids could flow through. We truly believe this helps keep the boards drier, making for less dry rot. 

I tried treating the boards with water sealer. The appatong was so oily itself, that it would not absorb the Thompson's water sealer.

I replaced the fenceposts in my outdoor riding arena several years back with pressure treated wood... supposed to not rot for 50 years. I hate to say that about half of the posts have rotted off after just 8 or 9 years. Most pressure treated wood is probably hemlock. Hemlock does not do well in wet conditions... often warping like your current floor.

One of the trailers I re-boarded was an old 1952 Miley. Great old trailer... and the floor in it was vertically laminated oak. It was 20+ years old when I ripped it out, and I was sorry I did. It was only surface rotted.

Best wishes with what you decide,

Coolie Chick