seam welding?

I haven't heard of people doing this for rigidity before but I will be doing it when I make the new pans for my 65 simply because I hate bondo. The car was pretty much supported in bondo (not kidding, the you should see the old rails) when I bought it. I guess I didn't contemplate the added rigidity because I dont have to worry about it with my full length rails and the 2 inch round tube cross in between them. I guess if you dont mind seam sealer or bondo on your car, leave it, there are much better, less expensive and less time consuming ways to add rigidity such as frame rail connectors and boxing the front rail to the rocker panel. Good luck in your project

The rear doesnt have as many problems as the front and center of the car. I'd work on the back after the rest was done.