Tow and pitch is another option some sites offer. Van is stored in a dedicated storage area on the site and towed out to a pitch when you want to use it then towed back to storage when you have finished.
You pay standard pitch fee while pitched and a storage charge for the year plus a small charge for the tow out and back.
Can be cheaper than seasonal pitch if you don't use it much.
Don't forget to leave a review of the campsites you have visited this year or last!