I am not sure what part of the Metro you want to stay in. If you want to stay on the west side there is Cotton Lane RV Park 17506 W Van Buren St, Goodyear, AZ 85338. There is a Walmart and a Target close by, or there is Happy Trails RV Park, a couple of the Forum members have lots there, at 17200 W Bell Rd, Surprise, AZ 85374. There is a Walmart and a Costco a couple of miles to the south of the park.
If you stay at Happy Trails, then head to Quartzsite, you can go back north a mile or two and get on HWY 60 and head west through Wickenburg on your way to Quartzsite. It is a very nice drive, and only a couple miles farther than I-10.
Also, there are a couple of ways to get to the west side of the Phoenix Metro. From Holbrook you can take 377, 277, 260 then 87 down through Payson to the 202, to the 10. Or you can take I-10 to Flagstaff then south on I-17 to the 303 around the west side.
I am sure others will have some ideas as well.