Most any automotive a/c shop should be able to handle that for you. Nothing unique about the dash air conditioning system in an RV.
Large RV dealers will have a chassis shop that can do most any repair to the chassis. Lazydays RV (Tampa) is one.
Some GM dealerships will also do light repair work on the 8.1L engine components.
Whether any of those will have prices you consider acceptable is another story.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC