I got my trailer and use a smaller than normal battery as I had one laying about. I'm a tent camper so being simple didn't bother me.
Convert your lights to LED light bulbs, there's some places on ebay that will ship you like 10 of them for about $10 and they draw a fraction of the power.
What everyone else said above
If you turn on - off the power to the water pump and use propane for hot water/heater, that helps. And don't blast the heat, just enough to make it tolerable and bundle up with hats and sweaters. Cook with oven, stove on propane. Fridge is on propane.
If you get a small or larger solar setup it will help recharge in the day, monitor battery voltage. I have two small panels and they output about .8 amps full power but did this sort of "reduced power" camping for 3 days no problem. And that was before I had LED bulbs, battery wasn't close to being discharged.