Just an FYI but you go about anyway you want but if it were me I'd be going under the trailer pulling the cover off and finding the screws that hold that frame in place so you can get rid of all the rott then finding were the waters coming from
I did think about that, but it seems like the hauler has the floor you walk on in the trailer, and a base underneath. It's like a box or something that encloses the frame. I am sure I'm not explaining it very well, but I can't see the rot from the underside without tearing undamaged wood out.