I have a trailer mounted powerwashing setup with a 1000 litre tank on it,..... It does the job, but I wouldn't want to be using it every day. Parking, turning etc etc is quite an ordeal, and even with the tank only 1/4 full it's impossible to manoeuvre by hand. Also the time taken hitching up in the morning, and packing up in the evenings is more than you'd expect.
Now I've got a bigger van I am genuinely considering a 2nd tank,.. another 400 litres that I can fill with pure water when I'm having a busy day on the windows,... tap water when I'm powerwashing,... and leave it empty in between!