I don't know that I would ever seal off a boiling pan/box of oil, for frying. Maybe this works in KFC's kitchen but not really in mine. It seems a bit dangerous. I think the seal on the frying box is probably meant to be used for storing oil but not frying food.
I have a pressure cooker, with a rubber seal, used for pressure canning, with water. I can't imagine it would be safe to use for oil frying.
Just one woman's opinion.