I would guess it depends how hot it is, my campervan fridge, which wern't that big would do a 2.75kg 907 bottle in 7days at sth France temps but that was with a bit of cooking as well. If the op has fridge manual that will give gas consumption in grams/hr so consumption over given period can be worked out.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.