[goransons]

I would say the biggest issue to look at is how much water has got in, if there is floor rot that needs to be repaired, if the bathroom has to be removed to replace rear plywood or repair rear end separation. If you manage to find one that you can stand on the rear bumper and not see tge seam between the frame and body get bigger, and that can be poked with a ice pic or screw driver around the perimeter inside (to check for soft spots) with mimimal issues, then you're probably looking at reasonable project, much to the same level of a home remodel of a few rooms. Just about any repair can be done, but know what you're getting into. Service Manual for a 77 would be helpful, and check the major renovations threads for trailers of that vintage to see what others have encountered.