I actually purchased the Propride hitch and had it drop shipped to the dealership. The Propride is several hundred less than the Hensley and comes with an adjustable towbar, with the Hensley you have to measure before you order and when/if you need to change it you have to "exchange" it with them for something like $200 (not exact here, hopefully I don't get beat up).
The dealership will struggle putting it together and most of them are incompetent by my standards (A&P Trained), but they'll do it to sell you a trailer.
If you have any other questions and would rather just call me let me know and I'll PM you my phone. There's not a lot of info out there with Land Rovers and towing and I had to make a few assumptions before jumping in. I have the fortunate situation of being very close to Land Rover Corporate folks and thus ran a lot of my ideas by my buddy who used to be the Tech Trainer for Land Rover (i.e. trained all of NA techs).
One other thing, I would consider changing your diff fluids prior to doing too much towing. The LR3 has a tendency of having problems there. We actually seeked out an LR3 with a rear locker as it's supposedly a stronger diff, and of course more fun off road! So far it's been a great tow vehicle. Only complaint is that there really aren't any good tow mirrors for it. I ended up going with the ones below after trying a few. Seems to be what most in the UK are using as well.
Grand Aero Towing Mirrors