How funny, I was thinking about the actual Popcorn Popper, you know the ones that have the door to open and you scoop out whatever popcorn you want, some come on wheels, like the ones at the MOVIES!!!! THAT WOULD WORK NICE!
You could cover the sides and back with mylar and change the lighting and just put your plants or seedlings in there!
now as for the cardboard box, Im not sure that would work if thats what hes talking about.