One more opinion for you...
Personally I'd get the furnace if you want it to be warm in there. If you're good with "backpacking in your truck" then you don't need it. Nothing wrong with backpacking in your truck -- it's simpler, quieter, and less expensive. I end up using mine in the winter and am not willing to do that, but your needs and preferences will dictate what you need. I tried a Wave 3 for a winter and it wasn't warm enough for us, but others seem to be happy with it. In retrospect, I should have gotten the furnace right off the bat -- doing stuff myself ended up costing more and using a LOT more of my time (partly due to how we set up the camper when ordering).
Yes you'll get condensation behind the arctic pack if it's cold enough. It'll drip down, and you need to get it dried out within a few days.
Electrical is not my strong suit, but
this might help with the truck connection.