Why would you need a Transit to work with a portable ? That is absolute crap. I and many others, including franchisees, run perfectly well with, little Diahatsu, Suzuki, Vauxhall, Renault, etc, small vans, which have room for two large portables, plus everything else, you need.
C/D have a number of those little vans.
They cost half as much as a Transit to buy and to run and they can access properties which larger vans can't, plus they can be parked in very small spaces.
When I started many years ago, I had a Transit sized van, but soon realised the problems which could easily be overcome, by using a small van.
So, my little Suzuki cost £5400 two years ago, does over 60 mpg, costs £80 a year to service.