On ANY "unibody" type car every part that is welded together that makes up the body IS the chassis. welding all the seams is a good place to start. as I said before any thing that can be done to tighten up the body is good on any mopar. I saw one company made a tube brace for the lower part of the rad support. welded on that would tie the two front frame rails together at the front. I hate to say it but the cars we all love are very flimsy. you think your charger is loose? try a convertible.