When my dealer wanted to charge me $600 for a hitch and "tow package", I about laughed in his face. Later, they were far from helpful (and perhaps even dishonest) when I tried to get an after-market hitch installed, but I figured it out without them. Here's how you can do it. This applies to a 2002 RX300. Cost: roughly $150 and 2 hrs of my time.
1) Go to U-Haul and have them install a hitch compatible for the RX300. They have a model that is an exact fit -- it bolts into the holes already provided in the Lexus auto frame. Cost: about $130. Time: 40 min.
2) Go to the web site
3) Remove the spare tire. If your vehicle included the "tow package", it should have a bright blue plastic box in the spare tire compartment labeled "Tow Assem. Converter". This must be there, else you'll have to buy it. If you must buy it, its quite expensive. If you have it, proceed to step #4. Reinstall spare tire. Time: 5 min
4) Under the vehicle, directly below the spare tire, you'll find a black plastic cover with three nuts holding it to the underside of the car. Remove the 3 nuts. This will expose a gray cable connector that the Draw-Tite #18245 connects to. Reattach the plastic cover and run the wiring harness/cable to the trailer hitch and secure it with zip-ties. Time: 20min
5) In the engine compartment, remove the fuse box cover. Look at the cover to determine where the 20-Amp fuse must be placed for the "TOW" option. Insert the 20A fuse (included in #18245). Time: 5 min.
Viola! Done!
I hope this helps someone through the Lexus Dealership hassle I endured.
Thanks. dkar