Some Questions :
1. Will 2 avg size batteries get me through nite?
3. I assume I need additional transfer switch, is there a multi source switch that can switch between mains, generator, and inverter?
QUOTE]
1. I use 3 group 31 batteries on my solar system. I solely use solar to power all 12volt power items and have not dropped below around 75% of my capacity. Typical 12 usage includes, refrigerator controls (propane when no AC electric available and AC electric for heaters only otherwise), lights, jacks, water heater controls similar to refer. vent fans in bath and kitchen. In the early spring and late fall, I also supplement the heat strip (in my rear AC unit) with the furnace using propane and 12V only. Typically, my 12v power usage is around 1000 watts without any inverter.
3. I am considering a hybrid Magnum, It has a transfer switch that will supplement power sources so you can use multiple sources at the same time.
https://www.solar-electric.com/magnum-energy-msh3012m-hybrid-inverter.html
Biggest delay in installing an inverter is keeping the inverter as close to the batteries as I can on a travel trailer.
My solar panels can recharge my batteries in just a couple of hours and still have plenty of power for daily use. Not sure that It would during the short, low sunlight days here in Iowa during the winter but it does keep the batteries fully charged all winter long with low power usage.