Ok so now that I have made a few box mods (14500 type) I am looking into building something a little more complex. I want to use an 18650 for insane battery life, but most of the existing 18650 mods are way above my price point. I would like to build one, but I need something fairly small, not too much larger than my existing 2AA Batt box mod. Anyone have any ideas or experiences on this to share?