I think Cave Gulch is first come first serve only, no reservations (location). Doubt space would be a problem there anyway. Out of the way, not on the tourist trails and a Monday. If needed, plenty of space for primitive camping and there is another CG up the road a ways. The USFS link does say you can reserve through the local USFS office. 50 person limit. The only other CG that might be a problem is Grasshopper, but again we hit it during the week.