While Krown will do nothing for surface rust under your paint, It will however prevent your floor jack from showing up inside the floor pan!

Just happened to my Corolla, poor girl has had cancer for years. Good thing I had another jack to jack up the jack. The first jack wasnt worth jack! - no more lat night replies

 

I generally believe in rustproofing, but I am concerned about all the holes they drill in order to apply the spray. Won't those holes decrease the rigidness and structural integrity of the car?

 

Mine's an 01, been winter driven all kinds. Never rust proofed, and even with the stone chips, never had any problems with rust. I also have the counteract system installed. Seems to be working.