Get underneath the trailer and inspect every inch of the floor from the bottom. you do not want to replace the floor. I would have someone hose the windows
from the outside and check the widows and roof vent for leaks
. I took my window our cleaned them and resealed them with butyl putty. $8500 sounds a little high but it looks like a lot of work has gone into this trailer. repack or have someone repack the wheel bearings.