I have the same as Mark Dew.
I have the tank in the van & carry about 5 containers for the trolley if i take it out off the van tank.
If you do run out of water in the containers just fill them up from the tank using the trolley.
I have a Freedom Trolley, Backpack, 250l Van tank, 1 x 18foot pole, 1 x 30foot pole, 50gpd RO, Water Butt, Hose & Connectors, Resin vessel for the van &containers for under £2000
Craig