What part of the lake do you want to camp at? Do you want to camp south by Katherines? Or further north? If you stay south by katherines there is one cove called telephone cove nv side, you can access it with 4x4 but it is by no means "private". A lot of people go there. As far as the az side by katherines I don't know of any that you can drive down to and camp. I have seen people on quads and trucks at some coves on the az side but have no idea how they got there. There are quad and dirtbike trails that lead everywhere out there. In September lake mohave shouldn't be too bad, just have to watch out for the monsoons that pop up in the afternoons. They will make it like the deadliest catch out there.
Thanks for the info everyone. These guys bring a pool table, dance pole/stage and a real bar, 25x25 dancefloor, shower rig on a trailer, plus a buffet for Sat. night dinner. Honestly too much more to list. So being able to be isolated is a must or "tourists" tend to want to get in on the fun. Ya they go waaay over the top, but hey go big or go home right? Some of the supplies were brought in on horseback at the last one in Silver Springs NV.