im aware that the steal will rot. alot of ppl dont want to take the time and money to replace a whole frame rail, yet with a stainless steal one that will cost ALOT of money. trust me it will be alot for the whole rail
this is more of a cap to go ontop of the arch of the rail and maybe 1.5 feet long from ither side of the arch. there would be about a 1/4 inch to weld between the top of the frame (where it mounts to body) and the top of the cap.
im not sure about you but id rather weld in stainless and cut out the old rust then weld in regular steal that will rust. on my car everything i replace is made in stainless so it wont rust out again.
if you want to replace the whole rail than fine, but thats alot of work and it will rust out because its made of regular steal.
if you want to patch your frame, the patch and the frame have a chance of rusting, but fine
if you wana put a stainless cap over it so all your risking is the welds to rust, even better
my thought was “the less there is to rust, the beter”