That sounds like de-lamination has occured. The usual cause is water intrusion (water leak), which is sadly a common occurrence with RV's. The best water leak detection is Seal Tech
. Trying to fix the de-lamination is useless until the source of the water is eliminated. Once the leak is sealed de-lamination may be repaired. This website is a valuable resource for the DIY type person: Repairing Surface Damage
There are several pages on that website, so look around. A man once told me he repaired such a "bubble" as you describe by drilling some small holes in the bubble, injecting them with the proper glue, then parking the MH next to a large tree. He then put a brace between the tree and the bubble to push it back into a straight wall. Never did know the result though.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"