Continued because of 1000 character limit.
There is a level spot at 18 48 18 N 109 17 12 W for boondocking and another small campground at 38 47 06 N 109 15 49 W. This one is kind of sloped but you could level out if you get parked the right direction.
Friends of ours stayed at an RV park just north of Arches NP a few years back. I don't recall the name but it was right on highway 191. They could ride out of the campground and access to the trails on the north side of the river like 7 mile rim. ATV TV has a lot of videos on youtube about the area or just look for Moab vids.
We boondocked at Hunter Canyon for two days. This gives access to Chicken Corners and Kane Creek Canyon trails. No aggressive riding, we ride like the old farts we are. It was a 20 mile one way ride out to the end of the Chicken Corners trail. It ends across the river from Dead Horse Point State Park. We didn't go too far up Kane Canyon.
The last two nights we were at the Dewey Bridge campsite. That is 30 miles of so East of Moab where the highway crosses the Colorado River. It was about 7 miles on the dirt road down to the Top of the World trailhead. There are some other trails between off the right side of the road as you are going down that don't show up in the guidebook. No hookups but there are vault toilets there. Onion Creek trail is just a few miles back toward Moab.