Our propane tank holds 10 pounds and that's all I can fit in the locker without modifications. So far it hasn't been an issue, because we only use it for cooking inside and it lasts us about 8+ weeks of light use when cruising. ("Light use" because most of our inside cooking is coffee in the AM and side-dishes for dinner, only occasionally baking or cooking an entree on the stove.)

We do use the 2 pound propane bottles for a Magma BBQ at the rail, and less frequently for the heater. Those are so readily available everywhere that I would hate to take away from the larger tank that is less convenient to fill. If we ever went cruising long-term I'd figure out a way to store a second 10lb or 20lb backup tank, but no need now.