Nick, I spent a bunch of time looking at the Twins design,
My line of thought would be to just skip modding the toter, build a 4 seat Argosy/sleeper unit that would still flip forward for service, and add a neat bed with a built in generator and bonus fresh water tanks.
then spend all the cool design features into a 53' multi level trailer with a garage in the back, and a roof patio. I just think by the time you had the truck all converted, you'd have so much invested in it, that if you ever wanted to upgrade powerplants you'd really be stuck. With a super trailer, You can always find a different truck to tow it. I'd even have a forward slide that once parked you could make the trailer even longer. spiral staircase, 4 side slides, all kinds of cool.
or start with a Pusher Tour Bus and convert that into something wild.
2001 GMC 6500 Topkick, 22' box, dropped frame, designed to fit into a 9' garage door. 3126 CAT 6spd Man Lo-Pro 19.5's w/ 3.07 rear axle ratio