Kinda like asking what house should I buy. Here's a few general pointers.
Sounds like you want to camp off the beaten path (no electricity). For the best life of the battery only drain it to 50%. Furnaces, nowdays, have to have fans so they drain the battery quickly. Mine lasts two nights and the battery is dead so to only drain to 50%, it's one night. LED lights are best for low wattage to conserve the battery. You could get a solar panel and a charge controller to put some charge back in the battery.
Get at least 4 inch thick mattresses for best comfort.
I have the small Coleman pop-up tent trailer. It is nothing to tow and I have taken it into some rough places. It's not big enough for a propane fridge. I have slept in it comfortably down to 10 degrees. You need a thick mattress under you for insulation, two sleeping bags, and someone to snuggle up to. I turn on the furnace in the morning to warm the place before I get up. Tent trailers are best for hot summer weather because they can be opened up more than a hard sided one.
Get a propane fridge. If you go back into the boonies, you don't want to be coming out every three days to get Ice for the cooler. A propane, AC and/or DC fridge is more versatile.
I'm fine with pooping in the woods but you need to check with the wife and see if she wants a chemical toilet.
Some trailers have a place on the outside for you to hook up the stove. This keeps the heat outside in the hot weather.
Get a screenhouse. You don't want to be cooped up in the trailer if it rains.
http://www.fleetfarm.com/detail/fiel.../0000000076868
Happy camping.