Hi.
20 years ago, there used to be a ton of areas to boondock. When we were up there about 6-7 years ago, most of the larger spaces were fenced off. Too much descruction and litter left, we were told.
We had problems finding a spot in a 26' Class C at that time.
Also, a ton of mud that time of year. Unless everyone in your group has roadside assistance, I would say the idea is not highly recommended.
It has already snowed there this year, so it possibly could be a very cold, wet winter. Possibly being the operative word.
Big snow time is Jan thru March. Maybe choose a lower elevation that time of year?
As far as the ATV's, you can take them on any Forest Road and on the side of the main roads. Starting in 2009 you now have to purchase a special sticker for $25, and the quads have to be registered of course.
They do close off a lot of the trails in the winter though.