I have not seen any "outside" pull down shades for an RV.
Seems the wind would give them fits going down the road.
I did make some 'outside' Snap On shades, but have not gotten to test them yet in any real heat. I did work in the Solar Shade business and know that they are phenomenal on homes.
I think what probably works best/easiest is to get some Reflextix and cut to fit on the inside of the windows. It worked well in the TExas 100 degree heat. But you can't see out the windows.
But, I think you are on the right track to block the heat before it enters the RV rather than try to cool it down after the heat has entered.