I am not sure I have a great answer for you – I checked the maps and it appears middle fork is a good walk from Whittleton. No doubt if it is too far to walk, you can hop on your truck and drive over the main area. My biggest concern - you will not have a full service on your first outing. It is something you can deal with, however. I suggest you contact the campground and ask the ranger their advice.
Ill post to the group to see if there are any cancellations. Let know if I can help else-wise.