i see this was revived by a couple posts over the last two days so i'll chime in for what it's worth
Waaaay back in the late 1970's i chose to live for ~2years inside a chevy hi-cube van with i think about a 10 or maybe 12 foot cargo box x~7ft high x~8ft wide. IT WAS FANTASTIC! I kept the rig completely stock-delivery-van on the outside and the cab interior with the metal sliding door between cab/cargo area...BUT in back? Way nice area to sleep/eat/shower/relax. I was the envy of several of my S.F.Bay Area friends stuck with high rent/mortgage when i was toodlin' around with my truck payment only
and my gym membership where i would typically play a round or two of hand ball then shower before heading to work.
I would do it again, though this time i would choose a long WB extra body Sprinter and keep it totally stock on the outside with only rear windows and the sliding door window...looking like a simple local delivery van.
Best wishes on your build, and thanks for your service (my two kids are also serving in the USAF and luving it)
OH, as a PS... i only had once silly incident (and remember this is in south San Fransisco!) over the ~2yr period. One Saturday nite while parked in a mall parking lot (my usual spots were mall lots) a car full of teens drove up and stole my gas cap! I think it was some sort of gang initiation or similar. Anyway i just let them drive off and they didn't even know i was inside the van. No one ever knocked or even walked the van as far as i know. never a bother.