An irritation and opportunity....Very popular state/fed parks will be booked about 364 days ahead of time as soon as the computer roles over the date. Folks have no problem paying the min reservation fee and then not cancelling if there plans change. There is some gaming the system that could be fixed by making the deposit substantial.
The opportunity is that the unclaimed reservations provide last minute openings. Talk to the camp host to id when/how these are released and you may find that a morning check in has openings as a result of no shows the previous afternoon.
pops