I think Lake Havasu and Yuma are the two hottest places in AZ in the summer. So I wouldn't choose those two towns. There's no question that the AZ summer heat will do damage as mentioned....fading of graphics, drying out of plastics, etc. In an RV I used to own, the little rubber bumpers on the inside of the cabinet doors melted and dripped onto whatever was beneath them. I would not leave any canned goods, or anything that could melt or explode in such extreme heat.
Perhaps look into Flagstaff, as it is at higher elevation and much cooler (as in less hot). Or there is a facility or two in Cottonwood, hotter than Flagstaff but better than Lake Havasu.