Looking good!
I considered using 2x4 wall framing but opted to keep the space.
If you look through my rebuild thread (in my signature line-Cowboy/Hilton), you'll see I tackled a very similar project.
Things I did right: Attention to insulation, vapor barrier, and adding a 1/4" extruded insulation board toward the interior (thermal break from studs and wheel wells). Sliding vinyl residential tri-pane windows (big improvement from the jalousie originals). Exterior painting (easy and looks good). Planning (I'll take a B+ on this). LED lighting.
Things I wish I had done: Plan for future solar power and additional batteries and pull wire before paneling. Install AC. Plan out storage solutions better (I could have made more and easier access).
You'll have a nice cozy rig if you continue along like you've done. I heat my 24' with a single electric space heater on low setting (I'm in MN, too). I changed the furnace to a simpler non-electric unit for backup, the RV furnaces are noisy and inefficient. If you're on a strict budget and can't afford new windows, you can always buy some insulation board and press fit into the window openings for colder weather.
Will be following along on the progress. Thanks for posting!
