As it happens, I don't think we were advised very well! In the event, we had no problems whatsoever. So long as you have a letter from your consultate that you have been resident outside Spain for over over a year (or possibly six months?), have NIE numbers and are registered on the padron (the person in whose name the shipment is - this was a definite requirement from the shipping company), and have a full inventory of the goods (they just used the packing inventory) there should be no problem. You have to sign a couple of forms for the authorities confirming that you the goods are more than six months old and that you will not sell them before a certain time, etc.
I must say, Crown Relocations dealt with the whole process, from Dubai to delivery in Estepona, including Customs clearance, etc., and everything went smoothly. I only showed up at the storage facility when the container arrived from Algeciras.
Didn't have to pay one euro at this end and just had to oversee the offloading into the storage premises!