I live and store my trailer in Arizona and you're right, the sun does take a toll. If you have a vent cover, it will help mitigate the heat when the sun is at it's worst. Just leave the vent open about an inch so if there is a dust storm your FW doesn't fill up with dirt. You won't need to leave a bucket of water in the coach for humidity. Arizona can get quite humid from early July to September due to our monsoon rains.
Make sure your tires are covered and protected from the sun. Although impractical, they'll be in even better shape if you can somehow jack up the rig and take the weight off of them.
I'd recommend you wax your RV with a UV protectant wax to help Prevent decal damage. 303 works well for many, but you need to reapply it every 30 days or so which won't work for you. I'd suggest Thetford RV wax which lasts many months before it needs to be reapplied.
Before you store it, make sure you have a full charge on your batteries and then disconnect them. Before hooking them back up again, you'll need to check the fluid levels and top them off.
Putting the insulation board in the windows is a really good idea because it will keep the sun from damaging interior materials.
Jim