I am assuming they are two 12v batteries - they should be connected in parallel - positive to positive - and negative to negative... and of course then connected to coach... ideally the positive from one battery and the negative from the other to help balance the load.
Sounds like you connected them in series - positive on one battery to negative on the other and remaining terminals to the coach - which put 24 volts into the coach...
I'm afraid you likely 'let the magic smoke out' of at least the inverter - and possibly other 12v devices that might have been on... Hopefully most were off. I would check your CO/Propane detector - as that is always on... and verify things like furnace, lights, fridge (if RV fridge vs residential) all still work.
(I assumed they aren't 6 volt batteries - as that wouldn't have had the results you mentioned... Two 6 volts would connect in series to produce 12v to the coach... Wiring those incorrectly would only produce 6 volts - which wouldn't have resulted in smoke...)