Looking for advice on purchasing a 3/4 or 1 ton pickup

You need at least 2" (4" better) of poly-iso insulation in the ceiling. 1"-2" in the walls.

You should consider going with no black water tank (compost/cassette toilet). If it was me and was planning on that much solar and batteries, I would not have any propane appliance. When you are plugged in and electric heater is fine. Find a 12V heated mattress pad (better than an electric blanket) and carry a buddy heater.