You want a good quality tint that blocks the UV light and heat. Just because a tint is dark does not mean it will block the heat better then a lighter tint. I have a 30% tint on the driver and passenger side front windows that has a 55% heat rejection. I have no problem seeing my tow mirrors or street signs at night. Federal law regulates the rear windows darkness. State law regulates the front windows darkness. This is you why you can get a dark factory tint on the rear right and left window of most trucks. The factory tint is legal in all 50 states. I added a light tint to the factory tinted windows for better heat rejection. I also tinted my sunroof. When I park my vehicle I use a sunshade on the front window which really helps keep my vehicle cool and protects my dash from the sun.
For any RV a good quality window tint would work out nice.
My window tint also reduces head light glare that reflects off my mirrors at night.
I use a 3m product.