Adding insulation WITHOUT tearing up the rig??

Shading the windows on the OUTSIDE, rather than the inside helps tremendously. I have done this with sheets and zipties for short term when desperate, but you can buy kits to make nice looking custom shades out of real shade cloth. Or put your reflectix on the outside.

And yes, if you can find a way to shade the roof that will be the other biggest factor. What about one of those portable carport things? Too $$?