All the outside fridges I've seen have been the standard "cube" refrigerator that runs on shore power only. If you're only going a couple hours from home then yes, whatever you've got in there will stay cold (provided you've cooled everything down before hand). But if you're looking for that to stay cold on a day-long trip through Georgia, Alabama, Mississippi & Louisiana in the summer then I've got bad news..........
Now if the dealer assured you that it "continues to cool as you're going down the road" I'd be on the hunt for another dealer. This one does not know his/her product, period.