We were in your position 3 years ago. Stock trailer, one battery, no generator and we needed the heater at night in below freezing weather at night. we didn't use the house light, using small battery light instead. The hot water heater was only on when needed. The furnace was at 50 degrees at night only. The portable TV, Mp3, dvd,laptop and phones were charged in the truck overnight.
After 3 day the grp 27 battery was down to 12.3v at resting and I knew it wouldn't make it so I turned the truck around, hooked a heavy set of cables and ran it for a hour a night. It kept the furnace going for the rest of the week.
I agree that a small amount of solar could do it for you if you get the sun to do it. A small folding kit could make up for a low power user or at least extend the time your battery will last.