I have my doubts, even as a 1 man set up you would struggle. 2 men (say 170kg) + 400kg of water is 570kg already, you only have 625 to play with. Say 20kg for the tank itself, same again for your leisure battery, 5kg for your pump. That is already overloaded and you don't have any window cleaning equipment in there yet, or any means of securing the tank. Oh, and don't forget your fuel, that is part of your 'payload' too.