additional capacity 'could' be added if you choose to add an additional bank of battery's and inverter. The inverters output would have to be dedicated, that is run separate outlets in the coach that come off the new inverter only. The two systems would not be connected in any way but increase the headache of troubleshooting if problems arise.
maybe there are some EE's onboard that could explain if the use of 1:1 transformers could be used to transfer the energy from a #2 inverter to the #1 electrical circuit (factory installed 120v circuit).
GO CATS