Bill,
When you talk to BG put their responses in perspective. They have some very good technical people, but I doubt if a single one of them has owned and lived with a coach. Your situation is a numbers issue. You have 2500 watts available if you are willing to push your inverter to the limit, and an AC unit uses at least 2/3 of them, (or if the current draw is close to Truk's all of them) nothing the tech says changes that.
You have only two options as I see it. Get a bigger inverter, and hope the Royale wiring was heavy enough so you do not have to pull new wires, or accept the fact that if you need AC while driving you will crank up the generator and keep the whole bus comfortable.
No disrespect to the salesmen, but I seriously doubt if any of them can get into the nitty gritty on this issue because you need to know wire sizes, if a remote needs to be changed, and how to balance the loads on the inverters so you can run all that you need while driving.