Ok observations from Malc Gold who three years ago went from trad to trolley, then added a backpack, then a 125L tank in his estate, then a 175L tank in his estate and then in Nov 2006 bit the bullet, leased a new doblo and put in a 400l tank.
In hindsight I should have gone for a van right away. I was working on a shoestring and unreliable cars forced my hand. If you can get credit then get a new van.
What I did right I got from this forum and it is the most important bit of advice I can offer:-
When you change from trad to wfp you must communicate that to your customers before you do it. In writing - twice. Once that it's happening and then again the first time you clean them.
When you do your last trad clean give them a letter explaining why you must change over. Dwell on health and safety, how they may be liable if your insurer will not pay out because you are using unapproved methods and you have an accident etc. Tell them how the windows will be left wet to dry to a clear finish, tell them the upvc will be cleaned. Do not back down on this. Dwell on the positive and warn of possible consequences - we all "know" what insurers are like! DO NOT be apologetic!
Switch over your round an area at a time. So that over about 3 months all areas will be changed.
I lost five custy's out of 220 - three were unavoidable (old georgian original leaky frames) two were because I was complacent and didn't do the above.
My average earnings per day are about half to two-thirds as much again what they were when trad.