Storage site is'Las Colonias' at Isla Plana - a very short distance from the Los Madriles site at Mazzeron (see CC book) Don't appear to have a website, but address is 30868 Isla Plana, email:
lascolonias_parking_caravanning@yahoo.es Tel. 968 15 25 31.
From leaflet I have fee is 31euro/month for van longer than 6m and/or TA. Van can be cleaned and serviced ready for collection. May be worth Googling to see if they now have a website. Several people (Brits) on this site near Mojacar use the storage regularly and speak well of it.
Undercover storage and good big accessory shop as well as workshop.
Some Spanish sitess also do storage but this tends to be in open air and not any more secure than overall site. Here they charge 1 euro/day so the isla plana place looks a better deal.