I'm in the process of removing and replacing rusted metal on my Challenger. Rails, floors, etc. Until this project, I have never fully appreciated just how flimsy these cars really are. Even the rockers and frame rails are thin gauge steel formed into pieces and spot welded together. There is really only one area of thick metal on these cars and it's the shock towers. Even the K frames are not as thick as you would think.
I don't mean to rain on your idea but I'd be scared to death to tow anything more than 1000 pounds behind one of these cars. If you were able to strengthen the car enough to actually make it work, the tongue weight of a 4600 pound load should be around 460 pounds. I just can't see the car safely handling that kind on load at the back end.