Sidewall delamination

I had a small delamination on the other side wall near the reefer vent. It was nly about 6-8 inches. In my case, if you pushed on the blister it would push in about  1/8 inch, but just where you pushed, not in any of the adjacent area.   Dealer had to grind it down and patch it. It was under a decal so they patched it and put on a new decal.  If it had been on the white surface I'm not sure what they would have done to match the rest of the wall.

I suggest you call Randy Mischler at the Crossroads repair facility. Even though you are probably out of warranty they maybe able to do some type of repair for an affordable price. I know they do other work besides warranty work there.

I have had the same delamination issue with my motorhome.  It isn't a water leak, in my case. I've kept track of it year after year by measuring it and it stopped expanding after a couple years.  I find it everywhere there is a heat source below it.  It is on top of my heat pump, water heater and refrigerator.  The heat appears to cause the adhesive that holds the outer skin to the inner foam to dry out and loose its properties.  Also, be very aware that on a very hot day, when sun is beating down on the outside wall, if you suddenly spray cold water (from a hose, for example) your outer wall can pop off the inner panel where it is attached by adhesives.

Larry correct me if I'm wrong but I believe these trailers are FRP (fiberglass re-inforced plywood) So you should be able to glue it back down anywhere on the side to the plywood. If I'm correct the plywood is still attached to the studs. This is how older trailers were built.