I'm approaching these stages and really questioning how much energy/effort/investment really provides a solid return, when it comes to creating comfort in summer/sun/desert like atmosphere.
The simple question is:
Would you rather have a typically insulated bus in shade, or would you rather have a foam sprayed, roof insulation painted bus in the sun?
Seems to me, in desert like climate, shade is the most effective form of staying cool. So, this means solar radiation through the windows and heating the outer skin of the bus. The bus only has 2 or so inches of roof insulation, and shy of paying for NASA like insulation tech, how much R value can you really get for your money. Seems to me, shade is the better investment.
I am building a lightweight roofdeck that will shield 35% of the roof toward the rear, then solar will cover much of the rest. Solar emits heat, but angled and shades the roof. I have a shade system which will swing upward/outward to shield the windows from sun.
My point is, investing in "shade" (roofdeck, swing up shades), then insulating with pink foam seems the "best compromise" approach, in tandem with a pair of 12k btu mini splits.
This is my theory...if you have experience and HVAC expertise, feel free to tell me how wrong I am, just also tell me why, so I can then agree and change course!