How to keep cool while (partially) dry camping all summer?

Make sure your RV is parked where it is in shade most of the days, open the windows, and use fans. It's pretty much how everyone lived prior to A/C.

Or, if noise is the only concern about running a generator, you can buy quieter models that will power an A/C unit and barely be audible inside the trailer or outside of your site. Not cheap of course.