And replacing the gas lines was rather costly and difficult for the dealership. The solution probably is to have the bottom power washed or steam cleaned before reapplication, and have it done every year. That may help, but gas and brake line longevity are a function of the material used and how they are affixed to the underside. I recently sold two one owner cars in the same week.
98 Ford Contour, 1 owner, 62K km, Krowned every year from new other than last year. Brake/gas lines in terrible condition, tight together and not well isolated from the floor pans. Everything fused together by rust. Gonna be a real mess$$$ replacing those. Matter of fact the entire underneath was very rough. Cost me an extra $25. for the safety.
92 BMW 318, 1 owner, 234k km, brake/gas lines from a visual perspective in much nicer condition because they were better isolated from the floor pan and I'm sure better lines.
So the short of it is that rust issues to a large degree are dependent on the brand, but for body panels Krown is well worth it on any vehicle.