I just don't get why that is a problem. You will have to pay at some time anyway. If one books a package holiday then one has to pay a deposit to secure it. It is what good businesses do. Of course they could make deposits optional. Those who pay a deposit will get a guaranteed booking those who don't take a chance that their booking will not be honoured. I suspect you wouldn't like that either. The fact that some members go away for lots of nights is not the problem of the club. They cannot treat people differently because they book more nights."A non returnable deposit will be taken with the option to pay in full or pay the deposit on arrival ." from post #198 (the OP) [italics my change] however not totally clear on the sentence.
Even if it is refundable I'd still be outlaying (potentially) >£1,000 in advance.
There are also a considerable number of commercial sites who don't allow this or booking has to be in same season \ year.
Another option is a higher grade of membership. for example one pays £100 per annum but does not have to pay a deposit on booking or £50 pa with deposit on booking. That is pretty much how Booking.com works. You takes your choice.