Here is one source - basically (or maybe exactly) the same as u-haul version. IPD specializes in Volvo stuff and while overpriced you can feel secure with what they sell. This is the same one I put on my 850 wagon.

http://www.ipdusa.com/ProductsCat.aspx?CategoryID=99&NodeID=258&RootID=629

If you look at the picture, only the removeable silver ball mount really shows unless you get on your knees. Drilling and bumper issues are for sedans.

And the one comment about the wiring is good - I hide mine in the little side compartment in the rear and just hang the connector out the rear gate when needed. Remember the car is only rated at 3500 lbs!

And if you are at all worried have uhaul or someone do the wiring. It can be interesting, and most problems are usually with the trailer's wires and a loose ground wire and not the tow vehicle.