Whether a month or a week it would not make any difference to those planning annual holiday. Also if a deposit scheme is introduced and you are limited to 3 bookings per annum, it may keep away those that like to book up every weekend for the year and then cancel at the last minute.One week only leaves time for last minute bookers to take over the pitch, no help for those planning/booking an annual holiday.
Perhaps if they lost the deposit after two cancellations, they would think twice about it. The C&CC plus many commercial sites seem to have managed with deposits for many years.