I sleep in my wagon periodically, usually for a night or a weekend and my only complaint is ventilation. Leave the windows down, bring on the bugs... leave them up, bring on the heat. I have seen a product that is a large screen that sticks to the vehicle from the outside but I didn't think it would hold up to mild winds so I made some window screens that slide around the entire window frame, when the door is closed it secures the screen.
The outside screen has a magnet running the length of the screen, helps weight it down and secure it to the vehicle.
The inside screen is flush with the door panel...
Both fold up for small storage...
Total cost was under $15.00 and about 1 hour of work.
1 - 36"x84" screen (I used Charcoal-Fiberglass screen), cost about $6.00
1 - 1/2"x120" roll of magnet tape, cost about $5.00
1 - 2" roll of black duct tape, cost about $3.00
1 - roll of fishing line (already had it)
Folded the screen around the template and cut, sewed the sides together with fishing line and sealed the seam with 2" duct tape folded over itself and the screen. Sewed the magnetic strip in with fishing line and sealed it with duct tape folded over itself and the screen.
They do their job well... I am going to make 2 more for the front doors.
The outside screen has a magnet running the length of the screen, helps weight it down and secure it to the vehicle.

The inside screen is flush with the door panel...

Both fold up for small storage...

Total cost was under $15.00 and about 1 hour of work.
1 - 36"x84" screen (I used Charcoal-Fiberglass screen), cost about $6.00
1 - 1/2"x120" roll of magnet tape, cost about $5.00
1 - 2" roll of black duct tape, cost about $3.00
1 - roll of fishing line (already had it)
Folded the screen around the template and cut, sewed the sides together with fishing line and sealed the seam with 2" duct tape folded over itself and the screen. Sewed the magnetic strip in with fishing line and sealed it with duct tape folded over itself and the screen.
They do their job well... I am going to make 2 more for the front doors.