i looked into these in a BIG when last year, when i started looking at WFP stuff
they will work for a VAN mount, BUT when you work out the cost int he end, i still went for a Trolley system, it might have cost a few quid more, but it wasnt that much more, it was only the cost of a sack truc or Trolley and a pump unit
you still need Battery, RO unit, poles, brushes