Don't use PT wood on TC.
The chemicals are poison and should not be installed in human quarters.
I am visual guy, so have hard time to imagine what you are talking about without a picture?
Most of TC have only aluminium skeleton, where lot of wood is still load-bearing.
That said, I had to shim my Fleetwood to go over new Ford sides, so having signs of weakening floor, I just screw 1/2" plywood under.
I live in dry climate, so water protection is not important, but you can use deck sealer for water protection.
