Tape it sideways on the top, or vertically on the side of the box, with the tube poking thru a hole in the box. You're lucky the rats were still in a cardboard box at all, they can chew right thru it- at least the small ones can. They might also eat some of the cardboard, which will end up inside the snake you feed.You really ought to spring for a plastic animal carrier with the ventilated top & handle to carry it with.