I just checked with the Lake Siskiyou Campground and found out that they only have about 9 large RV sites (with hook-ups) still available in the area ("300" series) where most of us have reserved sites.
If you are even "thinking" of attending.... you should reserve NOW to get a site. You can always cancel it later if you decide not to attend.
They also have large RV sites with hook-ups in the "200" series area available... but that is in another area of the park.
This group is "guaranteed fun!"....... you'll be glad you attended.