Can you call you supplier several days before they mail the monthly supplies and give them a current address. You can then use a general delivery mail address and pick up at the post office (check with post office first as some do not accept general delivery). Alternatively, you can use the address of the campground ( get the procedure and address from the campground office first). Alternatively, if they will ship UPS, then you can use the addres of a UPS store close by.