Those Double Tubes are cool too, you can make that for dual atts or 2 diff model adaptors
side by side, 1 momentary switch for activation and 1 slide 3 postions(ON-On) switch) for switching between 3,7V and 5V.Using 2X18650 in parallel and you need to use this PTN04050C you can get it free from TI (I got 2 from TI, I love this convertor, it doesn't even get warm, very efficient, no Resister just a 100uF cap required) . I would suggest Do Not use the 5V regulator in these tubes- too much Heat . Also when you put the batt's adaptors on the Tube, should have a hardplastic ring stay between the tube and the adaptor to prevent heat tranfer from hot atts-- My 4.8V mod got a little warmed when I constantly vape for a while, and I dont think that would be good for my batt so I plan to do that as well. I may get one of that DOUBLE for me soon lol
***One thing you need to know: that MOD gonna be heavy, and you may need to make a cap or cut and dremel the tube - hardest part for this mod.
Nick