Look it over with a fine tooth comb. Look in each cabinet for staining from a roof leak. look at the floor for staining and soft spots. Look at the walls for rusty staples or nails.
Lift up anything on the floor that is not factory and see if the owner is hiding something.
If the exterior is smooth fiberglass stand back about 30 - 40 feet and sight down the sides and front/back for big delamination bubbles.
Check the roof caulking. By now you should see where new caulk has been applied to fix minor weather cracking. Feel the entire roof to see if it has any soft/crunchy spots.
and if all checks out okay, see if you can sit on the toilet with he door closed.
Oh also test every appliance for correct operation.