I know Lexus says the car can only tow 3500 pounds with the towing package, but what mods can be done to the car to get it to tow more, and how much can it tow?

Eventually I will need a truck/SUV to two a trailer with a race car (not my IS... another ligher car), so I'm trying to figure out of the RX is a possibility or not.

 

I actually installed a 5000lb hitch on mine the day I got it. Heavy duty and somewhat hidden but mounted on factory frame without problems. Had to drill one whole in the hitch slightly larger. I believe there were six large mounting bolts. Even though it is rated at 5000lbs, I would think the SUV would be slightly stressed pulling that much. You need a Durango with the factory rated 7500lbs hitch. Friend has one with a dual axle car carrier and transported my lexus home from the dealer for me.