My trailer hitch was wobbly, when I carried 4 bikes on a hitch carrier, the hitch would move up and down. So, I quickly welded a support beam to a 3" angle iron piece that was bolted to the post that is below the spare tire. I also welded up the part of the hitch that was previously "bolt together" on the rear driver side. I know there has been discussion in the past about welding on the car. I disconnected the negative cable from the 12v battery and then did all the welding on the car. After welding, I hooked the negative cable back up and car was fine except for the gas guage which showed empty until I drove it for a 100 yards. FYI Lessons Learned: 1. Yes, you CAN weld directly on the car, just do as you would any other car and disconnect the ground from the 12v battery. 2. The hitch is much stiffer now for carrying bikes and eventually, towing a light trailer once I fab one up.
Heck, modding to add extra bracing and support is practically mandatory if you want the Coastal 2" hitch to work right. Hopefully Coastal does a better job this time around when they come out with a 2" hitch for the 3rd-gen. Their 2nd-gen hitch was one of the most poorly designed items to be inflicted on the Prius aftermarket.