making a stronger car

I was thinking of adding a roll bar, but I don't want to lose the back seat (yes, it gets used, poor saps). Actually, my first thought was to seam welding, but I don't weld, and I be it would be expensive. I already have sub frame connectors (kbdd from a long time ago), but the car still needs alot more strength. Any ideas? Maybe take a welding class? Also, any cons to seam welding?

Why do you want more strength?

You don't need one if you running above 11.99

You don't need one if you running above 11.99
lol, I like your sig...sounds like my car. :)

I am getting chasis flex that is now quite noticable. The car has lots of miles, so I expect that it is succumbing to all the abuse of 300k miles and lots of road courses has inflicted upon it. I mainly want to eliminate the anoying flex that I notice going over highways that are not smooth. It is most obvious in the seats, but I am going to remove them and check the tracks for play just to rule that out.

Check the studs that hold the seats to the floor. They are tack welded to the upper sheet of steel in the floor pan. I had two of those rip loose from the floor pan at very low mileage.