Not sure if you have these already in your coach,
but have you considered replacing your floor registers (heating vents) with some that can be closed off as in the house ???
Did that with ours and it seemed to be the final adjustment to
compliment opening the main grill so it initially dumps the cold air into the rv instead of cooling off the duct work running just under the sun baked roof
then as we (and the rv) cool off, we switch to back to ducted...
'11 Monaco Diplomat 43DFT RR10R pushed by a '14 Jeep Wrangler JKU. History.. 5'ers: 13 Redwood 38gk(junk!), 11 MVP Destiny, Open Range TT, Winn LeSharo, C's, popups, vans, tents...