I too have air suspension on a Transit Mk7 and it's superb. Mine was fitted professionally as I'm useless at anything resembling D.I.Y. I have a motorhome with a large garage and a longish overhang and we often carry two bikes on a rack, so there is a bit of a lever effect on the rear suspension.
It makes for a comfortable ride, the 'van is always level or slightly nose down and, depending on the load, a few swift strokes of a foot pump raises it. There's a gauge and an air valve just inside the habitation door for when I need to adjust it.
I've had it two years and done 22,000 miles and it's been fine. The brand is Air-ride and it was just over £500 fitted, but I suspect that you'd pay about £300 if you can do it yourself. You can get some that can be adjusted from a switch in the cab but I didn't feel that I needed that level of sophistication.