Peter Fogwills 2 barrel trolley was heavy enough, so I would imagine the adaption to 3 barrels would be difficult to say the least.
One of the problems would be if the customer has steps into his garden. We have a run of properties with on street parking and several steps on the path to the front and back of the house. This is why a single drum on a sack truck is better in those instances.
However, I did see a picture of a window cleaner in London doing shop fronts from an adapted 4 wheeled garden cart which carried a 125 litre tank on it along with poles, battery, controller and pump, a small hose reel, his cloths and a small A Frame ladder. He managed fine as he was on flat pavements with wheel chair access to cross the roads.