M2cW is get some triangles on that frame work or plates/gussets.
for insulation try polystyrene sheet instead of batts,
Factor in an overhaed console for 12v radio etc.
Sides big lift up doors with windows rear door window as well. Some sail rail for an awning
Just sold my one to my BFF
was 6x4 , 7x5 would be ideal. solar panel on roof acted as tropical roof
never got hot even in full sun,,,,,,,,,,bolt on /bolt off rubber in between