That is a solid idea. The GP kit has those tanks. However, I do not like built in tanks, I prefer a portable water supply that you can carry to the water source. In 2016 I had an elaborate food grade stainless water tank made for my Tacoma that fit behind the factory rear seat and was 13 gallons. I carried a 25 hose with me, but on one trip, I needed a much longer hose to fill the tanks. Plus, to me, the maintenance of a built-in tank is quite a bit more work to keep clean.
As for the upright fridge, I have built several vehicles with them, including my own which was in a German Made Camper and it had a 130 liter upright fridge. But due to the shelves etc, the upright fridge has significantly less actual usable space due to the upright nature. Think about the shelves in the fridge in your home, aside from boxy containers with food, how many things are stacked on top of other things in your fridge? You will see, there is quite a bit of dead space above and around items which eat up your overall liters of space inefficiently. I did not like the upright fridges and find that the typical top loading makes much better use of space.
The footwell space in my Grenadier is full of tools and recovery gear which is as heavy or heavier than the water that you would typically place there. Low and in the center of the vehicle for better weight distribution.
