One idea I had been toying with for maintaining two different size battery banks some distance apart is a dual inverter/charger scheme.
The main bank is hooked to your 12V and 120V system and has a combination inverter charger. The output from this inverter also feeds the input to a remote inverter charger on an auxiliary bank. The output from the inverter on the auxiliary bank feeds the input to the inverter/charger on the main bank (with some sort of transfer switch to disconnect it when shore power is available).
Somewhat complicated, but it ensures both battery banks are charged correctly for longest life. More expensive since you need an extra inverter/charger (but you save some on wiring if there is a long distance between banks).
Efficiency? Well, if each inverter/charger runs at 90% efficiency then the auxiliary bank would charge/supply at 81% efficiency. The main bank would supply 12V at 100% efficiency and 120V at 90% efficiency and charge it's own batteries at 90% efficiency.
If the auxiliary bank were supplying 12V at 100 amps through a round trip 40 feet of 2/0 wire (0.003 ohms total) then the power loss in the wire would be 100^2 * 0.003 = 30 watts.
If the auxiliary bank were instead supplying 120V at 11 amps through a round trip 40 feet of 12 gauge wire (0.064 ohms total) then the power loss in the wire would be 11^2 * 0.064 = 7.75 watts.
Of course the auxiliary bank has to boost the 12V to 120 then convert it back to 12V at the main bank, so the power transferred would be 120V x 11 amps x 0.81 - 7.75 = 1060 watts
At this point I realized it really wasn't worth the hassle, but maybe if you had a 80 foot long rig with 160 foot round trip runs...:D
