That sounds like a Clark County policy: Only one RV is allowed to be stored on each property parcel, so cover the rest so they look like big boxes rather than RV's and it'll be OK..... Chicken Little must have a hand in the rule making....
I agree, all it will take to "make bare fiberglass and holes in the corners of your roof membrane" is one decent sand storm. If you do decide to cover it, make sure the cover doesn't billow or move when the wind blows. If there's any movement, it'll "sand the trailer under it" and abrade the cover. Won't take long to see your cover investment turn to rags and your trailer "age before your eyes"....
Better off finding decent storage out of the sun if possible. If not, regular waxing, keep the tires covered and use it frequently.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS