If the vehicle is presentable it doesn't matter whether it is van or car on domestic or light commercial.
But having wfp and getting full potential from it means having a van.
When I went from trad to wfp I was using an estate car. I've used a trolley, a back pack and a 175L tank and barrels from it.
If you had a big estate with the seats down you could get a 250L in but that ignores the safety issues IMO. I even know one guy who had a 400L in the back of a 405 estate but it left very little room for the reel, pump and gubbins. He swapped his 400L tank with me when I got the van and he got my 175L tank and six barrels in return.
One of the posters above said how he earns so much in a morning and so much in an afternoon - that was a little less than I would earn out of my car with wfp. (I had a 175L tank too, remember). With the van the amount goes up appreciably because instead of driving back and filling and faffing (no insult meant - I did it too) and lifting barrels etc you are working.
Even if it is an hour that filling, faffing and driving costs you in a day then that is probably £30 lost.
Even so my Doblo with 400L is beginning to restrict me. I sometimes carry another 50L in barrels to top me up for the last hour of the day. My next step, planned for just over a year away is bigger van with a 650L/800L capacity.