Building a floor on top of Pressure treated trailer

[Nitrohorse]

Fist off, I've been a long time lurker. I finally retired from my job, sold my pop up, and now have the itch to build a 6x12 standy. I am going to buy
a 6x12 utility trailer that has a pressure treated floor. I'm open to suggestions as to how to build the floor. I was thinking of just using the treated 2x8 on the trailer as the bottom and frame out the area with 2x4s and use foam board to fill the area. I would then cover the framed and insulated area with maybe 1/2 plywood as the interior floor. I'm not sure I explained this well, but I am open to any suggestions. Thanks for a very informative site. It lead me to go outside of my comfort zone and build a camper by myself.

[QueticoBill]

Welcome to the non-lurkers!

I think you need to think more like an airplane and less like a truck. Ply on 2x4 on 2x8 - much unecessary weight. I'd go to 1/4 ply on both sides of foam, but few here would go that light, but maybe 1/2 ply on foam with 1x2 or 2x2 - and save many pounds.

[Nitrohorse]

Welcome to the non-lurkers!

I think you need to think more like an airplane and less like a truck. Ply on 2x4 on 2x8 - much unecessary weight. I'd go to 1/4 ply on both sides of foam, but few here would go that light, but maybe 1/2 ply on foam with 1x2 or 2x2 - and save many pounds.

Correct me if I'm wrong, but my concern was that if I place the plywood direct on the 2x8s, I could tramp moisture and have issues? I could rip PT 2x4s and use that as the frame between the 2x8s and the plywood. That would allow for air flow and lighten it up a bit too. I agree with you, I think 1/2 ply is sufficient. The trailer has a 3000lb gross, so there's some wiggle room for weight.

[JasenC]

Welcome aboard Nitro.

The PT lumber is going to have a lot of movement where as the plywood is far more stable. The 2x's are going to flex independently as well as the natural expansion/contraction of the lumber which is going to constantly pulling away from the plywood floor.

Can you use the PT to frame up torsion box and skin it both sides, that will be much more stable.

[QueticoBill]

Welcome to the non-lurkers!

I think you need to think more like an airplane and less like a truck. Ply on 2x4 on 2x8 - much unecessary weight. I'd go to 1/4 ply on both sides of foam, but few here would go that light, but maybe 1/2 ply on foam with 1x2 or 2x2 - and save many pounds.

Correct me if I'm wrong, but my concern was that if I place the plywood direct on the 2x8s, I could tramp moisture and have issues? I could rip PT 2x4s and use that as the frame between the 2x8s and the plywood. That would allow for air flow and lighten it up a bit too. I agree with you, I think 1/2 ply is sufficient. The trailer has a 3000lb gross, so there's some wiggle room for weight.

I could have been clearer. I'd remove the 2x8 pt to reduce weight.

[GPW]

A while back we replaced the "wafer board" floor on the FoamStream No troubles , as I found a lumberyard with " Clear and dry" treated 1" X 8". and it worked beautifully , no "slime". For extra protection I primed all the boards ( before installation ) with Glidden Gripper and haven't had any problems ... The floor is plenty strong enough , and the " drip edges " ( Thanks George) worked most effectively to keep any water, moisture or morning dew from getting near the floor ...