I think about the days off thing really depends on how long a camp session is. The camps I voluntered for, were 1 week long and we got no time off at all, while I worked at a camp that had week long sessions we would have weekends off-- from Friday at noon to Sunday at noon, with time off for a few hours at night.
The second camp I worked at had sessions for 10 days off, we had a full 24 hours off each session and 1 extended night off -- from 7 pm to 1 am off and a late night off from 9 pm to 1 am off-- we could not combine a 24 hour off with a late night off.
I would suggest possibly allowing staff to pick their time off at least for the teachers etc you have coming back
