Most of the handling improvements focus on the front and center of the car where most of the action is, but (short of installing a rollbar/cage) I like to see some inputs about improving the body/frame stiffness on the rear of the car.

Partly reason for asking is my own car has some sheetmetal rust-issues at the rear which I'm fixing as time permits, but over time I noticed (duh) how quickly the body structure becomes weaker because of this. Letting me to think even a stock (rustfree) body is just marginally sound to begin with.
Like, when I'm in the process of parking my car over a heavily crowned roadsurface and wheel on a curb, or when slowly avigating a speedbump at a sharp angle, I can sometimes actually hear the body structure 'work' at the rear because of the rearaxle and leafsprings putting more and less strain on the suspension-mountings.

I'm thinking, for instance, just like the beefy lower radiator supportkits available, the rear of the body could use some similar improvements aswell.

What say you?
Or, is my car really just a turd waiting to crumble and fall apart...