I built my own trolley system, It can carry up to 50 litres. The hose reel is mounted on it, I don't have to wheel it round the back.
If you have a very compact round, you can't beat it. What's easier, Pushing a trolley for 15 metres to the next house, or moving the van?
If I wanted a van mount I would just stick a tank in the back. Parking is a problem on new compact estates. With a trolley you can forget about it. Dai