We are looking at a 30ft class C that only has a 13.5 BTU AC unit installed with 30 amps power cord. We are concerned that this set up will not be sufficient to get through these sweltering summe...
To the OP, If you're talking about new rigs and have the option to order it with a 50 Amp option, I'd recommend doing so. You won't be sorry. Then, most likely, a second AC will also be an option for you too.
If you're looking at used units, then as others have said, you can install a rear AC with it's own 20 A cord. Note that this is NOT the same as 50A service. True 50A service will have two 50A hot lines (100 amps total...sort of) available.