I think you may have trouble finding a place.
Many of these parks will not take bookings from young people, or allow single sex booking (al males, all females)
For example the Haven web site says
Can we book a holiday if we are 21 years of age or under?
A) Haven and British Holidays Parks and their facilities are intended for families and adult holidays. We are therefore sorry that we cannot accept bookings from persons of 21 years of age or younger. We are unable to accept bookings for couples, or groups from this age group, whether single or mixed sex.