When I pulled apart my 68 Super Reverb tank to try to figure out why it wasnt working (bad cables by the way) I noticed that there was a cardboard bottom that someone had made and taped to the bottom of it to cover the opening. Is there supposed to be that bottom or is it simply supposed to be "open" in the bag? Should I be making a different bottom for it? Does thicker cardboard work better? Thinner? Just curious as I've never pulled a reverb unit apart.