I like it!
If you ever decide you want to make it more compact, you can use a plastic soda bottle (PET plastic) as a heat-shrink sleeve over the cells instead of the box. Very tough, especially if you add battery pack spacers (check ebay for your cell size) Here’s a vid of heat shrink action. https://youtu.be/9-L15mmZMmw?t=44
Do you have a PCM Protection Board in there someplace to help keep the cells balanced and stop under/overcharcge? Something like this: http://www.ebay.com/itm/LiFePO4-8A-Battery-PCM-Protection-Board-BMS-with-Capacity-Display-4S-12-8V-PCB-/182352477283?hash=item2a750dfc63