We usually have a two or three day journey from home to final campsite, and we manage to keep stuff frozen using two good quality cool bags, with silver foil inners and separate linings, a smaller one inside a larger. We put them both in the freezer to cool down for 24 hours, then pack them quickly, filling any air spaces with small items. We make sure that they are completely full - over the years making sure that everything to be taken with us is in suitable size containers. Each container is filled to the brim so there are no air spaces inside. We take several packs of frozen orange juice at the top of the coolbags - which is where stuff thaws quickly - and we put a layer of towel, tea towels, or newspaper over the top between the frozen stuff and the lid. We find things in the middle and bottom stay frozen until we arrive on site.
Things won't keep frozen in a caravan fridge and if you use it on 12v it will exhaust your car battery. You can't run it on gas on the ferry, and as the previous post stays it will only work on battery when plugged into the car with the engine running. You could, however, freeze litre orange juice cartons, remove any shelves, and surround any meat with them, and that would probably stay cold enough until you get to Spain.
BUT why bother - meat in Spain is cheaper than here - just take your sauce marinades with you, and make it fresh.
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