Rust on frame
Remove the driver's side gill and the lower rear inside wheel well. Then remove the battery tray. At that point a good body shop should be able to cut out portions of the frame that are rusted and weld in new metal.
The C4 frame is made of two C-shaped halves (front and back sides) and welded together. As long as there is good metal to weld, it's a fairly easy matter to form the pieces and weld them in. A shop with a frame jig would be the place to do it as the jig can assure the frame is straight and true when the welding is done.
Note that the part of the frame just in front of the battery has the last 10 digits of the VIN stamped into the front part of the frame and about an inch down from the top. If that gets cut away, I would suggest asking your state DMV or the state police if it can be re-stamped.






I think you better get a good frame shop to replace that weak section for you.

