On the west side of Phoenix, Glendale, Sun City, Youngtown, El Mirage all in the area of Olive to Glendale roads from 91st Ave to 137th Ave there are many of them Prices I don't know but I see them all the time I have ours (37') stored here at Pueblo El Mirage Rv Resort for now along with a (24') Enclosed Trailer and it's 68 a month. Hope this helps.
When we're not on the road we store our 36' FW along with the Ford F-550 at Arrowhead RV and Boat Storage in Peoria -- just off the 101 on Peoria Avenue. New place, both covered and open parking, but I don't know the rates offhand or if they currently have any open slots. But we like them. They also have a dump station and wash facilities.
I have a 28 foot TT, and I have plenty of room. The motor home parked next to me is longer and has the same space. There phone number is: (480) 893-3888. Give them a call to see for sure and check if they have open spaces.