We had exactly the same problem in a 2011 Southwind  that we bought new.  The squeak would often get so loud it drove us crazy.  It was worse when the temperature was colder and often quit when it warmed.  We must have taken it back to the dealer five or six times at least.  I finally wrote a letter to Fleetwood explaining all of this.  A factory expert talked the dealer tech through the repair.  I don't know what was actually done, but the squeak finally quit. Good luck.

We have the same problem. The second dealer helped it a lot by tightening the braces under the dash. The problem is the fiberglass dash rubs on everything. I think it is still unacceptable loud but not as bad as before. Looking for more solutions.

We got a 2017 Discovery LXE last year with the same terrible problem. First dealer was no help but second helped a lot by tightening up all the bracing under the dash. Most of this is accessible through the top cover plate. This did not eliminate the squeaking but helped a lot.

We recently purchased a 2017 PA 33D. It had an unacceptable squeak under the dash on the passenger side. The service mgr corrected  the problem by removing the dash cover and sqirting baby powder around the area where the dash meets the windshield .  He also found under the hood on the passenger  side a medal shelve that was rubbing against the fiberglass and he bend the edge so it did not rub..  That completely stopped all the squeaking.  Maybe this will help.