I consulted my ‘resident expert’ and he said that your best bet to protect the plywood is to find yourself some WHITE paint (for the most reflectivity) that is house paint with the highest UV rating you can find.
Since you live in the desert, you probably should be able to find that locally because it would be pretty standard for house paint in your area.
My advice? Always find the OLDEST geezer working at the Hardware Store and ask HIM what to do. ;)
Thanks for the geezer tips. I’ve already learned that the older clerks are chockful of geezer knowledge. They also have more patience with women of a certain age and their wacky little projects. The younger guys are great for carrying the lumber, PVC and Quikrete out to the car.