My opinion ...
i think the Sig pistols that were designed, manufactured and marketed for military, law enforcement and other professionals are top notch. To dismiss and avoid all Sig products because he doesn't "trust Sig" is a bit of a broad condemnation of one of the best firearm makers available.
I used FrogLube on all my pistols. None have any rust. I see some of the ones I own being reported to have rusted for other owners. As always, not all guns make it out of the mill identical to all others, and the conditions of carry, use and storage vary among owners.
Having said that, I see quite a few posts of people reporting rusting 365 mags on other forums. Those who contacted Sig were provided immediate replacements.
The pistol itself doesn't seem to have as many reports of rusting, but there are some.
Still many others have reported to own a 365 for years -- for carry and not -- without a single problem with finish or rust.
It may be that Sig decided to change the composition of the finish material or the process of applying it to save money. That's a normal business decision. They know if they made any changes, and they are aware of these complaints. If enough people make this issue public, I'm sure Sig will correct it if they can.
Personally, I don't trust any gun maker to counteract the effects of time, elements and use/abuse on my firearms, so i use the best dry metal protectant I can get. If you follow the directions and use the proper amount of heat to bake it into the pores of the metal, FrogLube not only protects during storage or carry, but it will partially liquify from the heat of firing creating a smooth, friction free coating.
I'm not selling FrogLube, just saying the owner needs to take rust prevention seriously and not leave it all up to the factory finish.