Also concerned about the final weight with 2x3 framing and plywood exterior.
Have you checked your door frame or glove box for your payload rating on that truck?
Are you doing a full build out on the interior: cabinets, sink, fridge, water, propane, bed, etc.?
I admire your fortitude to take this on but I'm worried that you may not be happy with how that truck handles the load especially with a 4 banger.