IPD sells the drawtght hitch which is what I have on my 92 906. It does tuck up nicely under the lower bumper skirt which needed to be cut out on mine. The hitch is pretty easy to install. If you don't feel comfortable about the electrical part, it's worth having it done at the dealer or competent garage. I bought the (volvo) electrical wiring lume and had it installed. It also tucks up under the bumper. Since it's a Volvo product, it's connected under the dash with no imbalance in the light sensor to annoy you when you apply the brakes or turn. I couldn't be happier with my setup.

And, of course, driving the S/V90 witha trailer is hardly noticeable. However, if you're drivng in hilly terrain, you hould keep it in 3rd and under 60 MPH.
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John Shatzer, '92 965 @100K; one of a few still in captivity.