Sounds like he's doing a lot of hard work for not a lot in return. A good day would be £200, 55% to (the guy who's robbing him), sorry, the guy who he's working for!! Why would you pay somebody for working for them! Then £15 a day for the van lease!!!
So he comes out with £80 a day at best, does he have to pay for fuel and chemicals as well.
Think I need to rethink my business model.
What van is it? Keep the system in the van and add oven cleaning, you can do both from one van, that way he can help you with windows when busy and do ovens as you build it. Target your customers first, you'll be amazed how many will use you for both services.
Good luck.