I've used one of these boab 40L tanks squeezed behind the passenger seat and underneath the fridge.
Seemed a convenient place for it since I'm always opening that rear passenger door to get to the fridge anyway.
Both me and the Mrs are fairly short-arse, so don't need the seat all the way back, which would be a limiting factor to fitting this tank in the space.
Pic shows a trial fit before I bolted those track rails to the floor (with a support plate on the underside) and strapped the tank down.
Tap is just gravity fed.
I've also got a separate 20L plastic Jerry with the same style of hose/tap coming off the bottom that can stand on a table or on the rear step of the Def.
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