Custom tanks would work fine for fresh water and gray water. A black tank needs to be designed without nooks and crannys. Not to say it couldn't be an odd shape or be stepped.
A B-Van could be fine for full-timing as long as you have a minimalist lifestyle. Personally, I can't stand a campsite that has clutter about - looks more like a refuge camp than people on a fun vacation.
I'm constantly editing what I carry around. I've gone so far as to prepare totes for specific type trips - beach, mountains, tailgate, fishing, etc. - so not everything has to be carried every trip.
