It depends on your model, and accessory package. Mine has the jack. Some have heat/ac parts, and something else I can't remember. On those, the jack is back in the right rear corner, in view.......the front passenger seat? If you were to remove the stock front passenger seat (to create more space) what is going to be left potentially in the way?
Here's a link that shows my custom bracket, at the D pillar base: http://www.fordtransitusaforum.com/...0-project-minimalist-kayak-14.html#post298177
The reply just after that shows an OEM mount, at the rear side wall.