Norman, Is it a bulge or a bubble? If it is a bubble it probably means water got behind the outside siding and the main wall and the glue came loose and it has bubbled the outside. First thing you need to do is check to see if you have any leaks going inside the around the window (remember, water takes the path of least resistence) and fix that. Check your roof to make sure it is sealed good. Basically check anywhere that water might be able to get in, including your inside plumbing.
I have a similar problem that was caused by the previous owner letting the frig defrost to the inside and it got behind the siding and caused bubbles. The only way that I can really get it fixed is to cut the bubble, put construction glue behind the bubble and hold it flat (with clamps) and then fix the cut. Have to cut it because ya can't get the bubble out unless you do. Of course, you could take it to a body shop for RVs and get an estimate on repairs.
In any case, it is not an easy repair (depending on the severity).
Hi Norman, again Archer is right on! Generally the way that the walls are made is this the inside wall is luan paneling next is about 2" of styrofoam and then more luan paneling this is sandwich/glued togather and installed on the rv then the fiberglass siding is glued to the outer paneling and the windows / compartments are cut out and installed if the seal around the doors and windows doesn't hold, water gets in and either or both the glue lets loose and the luan paneling rots either way you get a bulge, that is very difficult to repair. As Archer said check the roof & windows etc for voids in the caulking and recaulk & reseal with a sealer :laugh: . :bleh: :approve: