I am not sure I am understanding your question. As another poster stated, your signature reflects that you own a 5th wheel, so you must have an RV refrigerator. You should be able to keep milk at least a week, maybe even two weeks. Isn't that long enough?
Make sure your RV refrigerator is cold before putting any food in it. We plug our frig in and I fill up our ice cube trays with water. Once we have solid ice cubes I know the frig is cold enough (usually over night).
When you buy milk, check the sell by date. It should be out at least 4 or 5 days. It will keep if refrigerated 7-10 days past the sell by date. Check this site out for more info:
How long can you keep milk