Sorry, I can't help but I feel your pain. For every stellar dealer/repair shop there are a dozen or more ranging from sorry to downright criminal. You might try an aluminum company or mobile home supply for parts. I know our local aluminum place installs 4 season rooms on decks or patios with insulated doors and windows, and claim they can custom fit most anything.
2015 Crossroads Cruiser Aire CAF27RL, 2018 F250 diesel crewcab SRW 4WD short bed, Trailer Saver hitch with Reese adapter on Ford OEM underbed 5th wheel connector.