1. I have 50 years in the RV industry. NEVER heard the term "Fishbowl". WHERE did you get that saying?
2. I would try to get a 2 inch type Dash AC flexible hose and fabricate a way to connect to the forward Roof AC AC vent and use clips to allow that cold air from the Roof AC's to blow cold air up to your "Fishbowl". Also, you don't state, but just what is the Dash AC output temp at 60 mph on MAX/Cool? It should be under 60 degrees closer to 50 degrees. If NOT, then that is your problem. I doubt your driving temps are lower than North Texas in the summer(90 to 105). I never have complaints from my Customers that after the roof and dash were working to spec, they could not stay comfortable. We sold Mandalay 15 years ago and never had cooling complaints in transit during the hot summer months. You probably have both roof and dash systems not to spec. Doug