Just a thought, why not make a tube mod with a magnetic 'door' to replace batteries. Could be an actual section of the tube, you know like splitting the mod in two - or other proportions - to access the battery. That could also enable to use new button types/systems I guess? Or maybe a shorter mod, or stronger connections. If I would have my pick, make it top firing button and regulated, either fixed voltage or variable. It's the same for me. 
