Henry, That brings up another point I had forgotten to mention. I work at Fort Dix, US Army base in New Jersey. The DOD Police (Dept. of Defense) are using the new Chevy Impalas which most of you should know is a unibody construction. The cars are not holing up from the daily use. Many of them are having body problems like what you mention with your unibody cars. The Ford Crown Vic's which is a body on frame design held up much better. I've talked to the New Jersey state troopers who uses the Fords, and don't have the problems they had with the unibody cars in the pass.
Just another thought I wanted to mention.
Rich Woolf