on my shasta tt i have removed the sheet flooring and found OSB wood that was water soaked under the board i found sheet metal that was rusty and wet and in pieces i am replacing the wood with plywood do i have to replace the sheet metal to protect the wood under the trailer
Metal bellies are infamous for causing floor rot. Try to clean all the insulation out of the floor space and use styrofoam to replace it. (doesn't absorb water) I've gone as far as drilling 1/4 inch drain holes in the belly to try to prevent water damage... Not sure it that's the thing to do, but metal also sweats, adding moisture.
Also, if it doesn't get wet, it won't rot. The water is coming from above, insidiously running down inside the walls, and ends up in the belly, forming a nice rot soup. So, if you re-putty the edge trim/J rail, windows, doors, etc, that will go a long way toward a dry bottom.
You should be able to trace the water path when the skins are lifted for repairs.
thank you for the info i tracked the water issue it was from the front window which was so called sealed with caulking (previous owners) not putty i am replacing the front wall wood due to this pictures will be soon