Here's a quick way to pre-screen boondocking sites in the Moab area. If you are within 30 miles of Moab, if you don't see evidence of a lot of camping spots on the other side of a wash, don't try it. In the Moab area, things get crazy busy and every potential spot is filled on weekend in the spring and fall.
Of course that doesn't eliminate spots where the sand consistency is, well, inconsistent. For instance the Willow Springs road heading the back route into Arches NP has a sand crossing that can be no problem at times, but in the spring after weeks of car, 4x4, motorcycle and ATV traffic, that crossing gets pretty deep sand. Not impassible for most vehicles but no way I'd attempt to take a trailer through it.
Hopefully you've discovered the BLM map showing where one can and can't boondock.
Moab BLM camping map PDF Note the blue areas on the map. Those are state lands not impacted by the BLM restrictions. That's why the Willow Springs road is so heavily used. Utlimately it becomes a choice based on the balance between wanting a degree of privacy vs. how far one has to travel every day to get to the parks, the hikes, etc.
