Bill,
For some State parks there is a Reservation site called: "
Recreational.gov "
Here is the Link:
http://www.recreation.gov/welcome.do?topTabIndex=Home
Once you do a search for the state and location you want to camp... then you can narrow down the actual site... by looking on their Campground Maps... they list the length that will fit on each site... they list the electric hook up - 15 amp - 30 amp or 50 amp. They list if the site has water and if it has sewer. If you have camped at state parks before... you might know not all have electric and water... and not many have sewers... but some do.
To be clear, this site what some states have selected for the reservation service... but not all states... and with the ever changing level of state support for their parks... who knows if they will continue using this service.
I believe we'll be seeing more and more State Campgrounds closing because of funds have dried up from the State level. I hope I'm wrong...
As far as Yuma... I've been there a couple times... Boon-docking is not site specific... I mean to say the sites out on the Desert are not sites as we would know them... as in a RV Park. they are just where ever you feel you can park... and as much space as you need. Most folks don't snuggle up against each others trailer. Well, except for Quartzsite Arizona... I've parked there with the Escapee's Boomer's group... kind of close together... just so we'd not have all that far to walk to the 4:00 PM social hour !
I have never yet found a park in Yuma who couldn't handle my 3400 RL BigHorn. There are plenty of parks there as well as the Rio Grande Valley of Texas. The sites are plenty big enough... most with good services... and the SunShine can't be beat !!
But remember those areas get full pretty quickly... I have also found they Love the RV'ers who commit to a 4 or 5 month stay... and are reluctant to commit a site for 3 or less months... at least they are early in the fall... as January approches... they change those thoughts for anyone who'll fill the sites they have empty for a couple months.... This has been my experience at least...
Hope this helps some... Good Luck !