Anything is possible but to earn that you will need the appropriate amount of customers and work at a regular speed.
Ive been going 6 months now and only now i can say that i have easilly earnt my days wage. THis is down to technique and how compact the work is. For example last month i had my best best ever day which was £155 and did 13 houses, but i do not earn this everyday, either because i have a little more driving to do or some of the work isnt as well priced as that day.
In the begining for me it was hard, some days i would only earn £60 and be out for 10 hours and thought how the hell was it going to work, but down to trying to get it compact as possible and 6 month experience it is finally comming together.
So i would say canvass canvass and canvass, it wont be easy to start with but to do it full time you will have to give it your FULL attention, probably not possible doing weekends only.
My average hourly rate is now between £16 and £20 which at the start i didnt think was possible but it is.
Oh and i am a traditional cleaner, laddes and a squeegie love um!!
Remember you probably will not work the full 20 days 8 hours a day either cause of weather, odd day off, not enough work etc etc at for the first few months while your building your customer base.
hope that help a little
Andy