The best place for a portable is just outside the customer's door.
Van-mounting a powerful portable is possible, but you will still get times when you either have to get it off the van, or turn the work down - maybe not many.
You have hoses going across gardens, and vac hoses are very hard to clean, so you get an inside hose and an outside hose. Then you got the extra solution hose, and the solution cooling down before it gets to the house. Then you've got to hook up to their power, which if you're running a heater on the porty means 2 leads.
Folding aluminium ramps must be worth a try - the longest ones that fit the van would give you the shallowest incline.
Lastly spend as little on equipment as you can - doing the jobs is the easy bit, making the phone ring is where you need your attention as much money as you can get.