You can also check out
www.Glamisnorth.com. It is an RV park on the opposite side of the Salton Sea as Ocotillo and a very family friendly place. There is a rental company that rents quads and side by sides out of there. It is still a 30 mile ride to any sand dunes and you are still quite a ways from the main part of Glamis. There are some other cool places to explore around there too depending on your interest.
We go to Glamis on non holiday / slow weekends and most of the time find we can avoid the crazies. We haven't taken our jeep there yet, but have seen several out there and would like to try it one day.