We got four sets of keys with our trailer. We have to use two separate keys for outside storage areas. We have the slam latch style cargo doors at the front and then the large cargo door in the rear. I am guessing that the 4th key we have not used yet goes to the outside shower.
I too have a smallerkey that looks similar to the deadbolt key; it even has the black plastic trim around it. It doesn't fit anything. The outside shower is the usual 751 key. The slam latches have their own separate key.