Greetings Marsh,
I have stayed at the following places on this route.
River Breeze Resort LLC, Ehrenberg AZ. Full Hookups.
Lost Dutchman State Park (east of Phoenix, AZ). Water and Elec, Dump Station
Apache Junction KOA (east of Phoenix, AZ), full hookups
Catalina State Park (near Tuscon, AZ), Water and Elec, Dump Station
Las Cruces KOA (west side of Las Cruces, NM), full hookups
Balmorea State Park, (near Balmorea, Tx) Water and Elec, Dump Station
Fort Stockton RV Park (east of Fort Stockton, Tx) Full hookups.
These are not boon docking or free sites, but I would do them again.
Enjoy your E21 and Safe Travels,
Ken