Just wanted to add one safety issue with this stacking thing. Vent holes. It is wise to have them for the just incase things went bad scenario.
http://www.e-cigarette-forum.com/fo...s/76078-exploding-mods-current-situation.html
Found in that link
"
Gas vent holes
Holes must be drilled to vent the gas that might result from heavy charging or a short-circuit.
A minimum of two holes are required, each of which must be of 2mm diameter or larger.
Radially-drilled holes are preferred to holes in the end of the casing, since if they are in the end then the mod will be propelled strongly in the opposite direction, perhaps toward the face. Radial holes (holes around the outside, probably at the lower end), are preferable as they will not impart any thrust during a gas vent incident."

on safety