The ProMaster has the most generous wheel-well voids of the three major vans, which is why every tank here is 28 gallons - a third more than the equivalent Sprinter or Transit tank in the same location.

Fitments are PM-L-28 (left), PM-R-28 (right) and PM-C-28 (centre). Run left and right together for 56 gallons with balanced weight and no lost floor space - genuinely rare capacity in a van this affordable. The centre tank fits between them under a bed platform if you want more.

Remember that 56 gallons is roughly 465 lb of water sitting behind the front axle on a front-wheel-drive chassis; check your payload before filling both. Add a 12V/110V water heater and see the full system in Van Water Systems.