If people could see pix of the mug and handle they'd probably suggest another way to do it, like drill, tap, and bolt, or perhaps welding then grinding. With a thunder mug, at least if I were doing it, I wouldn't be at all worried about drilling a bolt holes top and bottom. Holes are drilled in a lot of cannons for all different reasons, often for sights etc., and it doesn't seem to be safety issue. I'm guessing the practice is ok if the hole is not too huge and if it doesn't go all the way through the wall of the cannon tube, but I'm not smart enough to give you a rule on how much of a hole is too much.