Seven nights minimum sounds pretty excessive for a break that for most people lasts no more than 3 nights. It may be worthwhile calling their bluff on this one: last Spring Bank Holiday, we had not expected to be able to get away, but at the last minute found that we could. After phoning around, we only found one site that had vacancies, but they wanted a four night minimum. We refused to book this, but left our phone number with them 'just in case'. Within a couple of hours, they were on the phone, saying they had spaces and could, after all, accept a two night booking! So don't give up - if Easter approaches and they still have spaces, they will probably be glad to fill them for as many days as they can get!