Randy has it right; maybe I wasn't very clear.
The (electric) furnace fan is on about a third of the night during the winter, so I have to plug up to shore power every few days to charge the battery
. Furnace IS great BTW; when I wake up it's 70-75 degrees!
In summer, I use so little electricity that just driving keeps the house battery
at a pretty good charge.
In winter, when I know I will be discharging the battery pretty low and won't be driving much for 2-3 days, I make sure to unplug the trailer from the truck whenever parked, or the trailer will use the starting battery to charge itself (leaving you nothing to start the truck with!) Learned that the hard way!
The shower still works great even when the battery is low. You can tell you're depleting the battery when fans slow down, water pump sounds different, lights
are dimmer, etc.
Put as full a charge on the battery as often as you can, and you're fine. The Interstate size 27 that came with the Casita
has been great for a year and a half now. I check the acid level about every three months and add only distilled water when necessary.