A truck cab with a hicap tub is much more useful than a disco without any seats in it. If I had a hicap Id make some kind of demountable camper, although probably not the traditional kind that looks like a caravan dropped from a helicopter with great accuracy, it would probably be a plastic canopy cover with some boxes/shelves that slide and bolt in - Ive not given it too much thought, since kitting it out is the easy bit, getting the base vehicle to exist is the tricky part in that instance.
For a 7 seater disco, the way Id do it is this - a drawes/box under the 2 rear seats permenantly. That leaves the seats availably for use, and if they arent used, the "footwells" of those seats makes useful storage space. Then Id also have a reinforced sheet which is stored agains the back of the middle row of seats, so in normal use, youd barely notice it, but when the middle row are folded down, it fits behind them, on top of the 6th and 7th seats, to make a flat bed. Theres some space below that platform in the boot, and, although inconvenient, the front seats can be used, and if its just me in the car, theres plenty of room if I put the air mattress to one side. How much stuff do I actually need? Id put tools and some recovery bits in one of the drawers, and cooking/camping/etc stuff in the other. Bulky stuff like camping chairs, folding table, or a tent will fit in the boot under the platform.
Obviously there are limits, if Im trying to take 7 people camping for a month 500 miles away from the nearest petrol station, then Im going to need a roof rack, or a trailer. But realistically, 1 or 2 people most of the time, and having the option to carry more occasionally is useful. I can count on one hand the times that Ive used the rear 2 seats, but then thinking about it, if I only had 2 seats, Id probably end up buying another car with at least 4 seats in it.