We ended up going with an inside shade vs outside, and held on with suction cups. Works awesome, we have one for the front windshield and one for the driver and passenger side windows.
We also picked up the windshield visor - not for the front, but for the sides, you can put them on when you are traveling and they help block the sun.
RV Recreational Vehicle Window Shades Blinds Curtains RVQuickShades.com
They can be cut to size - we shortened the ones for the side windows, but didn't have to do anything for the windshield.