SHOULDVE SPECIFIED HOW DO I mOD THIS LOL
It would be very large as far as mods go, but it looks very durable. Pretty much the way you'd mod anything - carefully gut it and salvage usable parts, machine needed openings, implant electronics, enjoy succulent vapor from a self-made techno-wonder.
You'll probably need a rotary tool, soldering iron, electronic components, batteries. I second the 26650 notion...
I could suggest what parts to use if you could provide the dimensions and what you're willing to spend on it.