I have had 3 sig pistols form rust on the triggers in the past 2 years.   2 were p365 (one is the rounded teigger the other is a straight trigger they put in for me) and a p365xl which comes with their straight trigger.   I have numerous rifles and pistols with metal triggers, I shoot 1-3 times a week (regardless of winter temps) and I never wear gloves.  I use fp10 oil and have never had an issue outside of the sigs.   My west german p220 has never had this issue.  The rust isn't little dots it is large patches of aggressive rust, it forms in a week or less, and I would like to prevent this.  Ive considered just buying a stainless aftermarket trigger, I dont think I can put enough oil on the trigger to completely prevent it at this point.   Does anyone treat their gun with something to prevent rusting outside of oil and maintenance?  I brought this up in the sig forum and they took it as an attack.  There are posts online with other people experiencing rusting issues but people generally just blame the gun owner.  I get that, but it should mean you would find rust on my ar triggers and other pistol triggers I shoot a lot more than the 365s.   Just looking for ideas on chemicals or treatments to prevent this in the future.

My personal 365xl has been good to go.
however I have A coworker that was complaining of rusty magazines on his 365 sas.   upon further inspection and break down there was also significant rust on the slide and the retaining pin that holds the trigger housing  in, and magazine release and magazines.
Cerakote was the cure.

Apply oil.
Rub in.

I usually take a new pistol down completely.
Strip off the 'storage' grease.

Warm all parts in a toaster oven at about 250F.
Drop them into Break Free CLP.

Allow to cool immersed in oil.

When they are cool, fish them out and wipe away excess.

Reassemble with conventional oil and grease.
I am looking for some 'wear in' on mating parts.

Shoot a thousand rounds or so.
Clean it all off again and heat and cool in Break Free CLP to put a nice film on them.

Put it all back together using Mobil 1 oil and grease.

Wipe it down carefully and thoroughly.

Ready for another range trip.

Brickeyee, while I appreciate that your maintenance schedule should protect any carbon steel from rust it is pretty extreme.  Ive read police and military maintenance manuals and I've never come across a process similar to the one you have set out.  I sell both carbon steel and alloys for a living, this issue could have been solved by selecting a different steel or like the other poster mentioned cerakoting the parts if they are mim or basic low carbon steel parts.   I oil the trigger after each range trip, I wear plastic gloves while cleaning and I wipe the gun down before applying fp10 oil.  A quality modern pistol shouldn't, and doesn't require an extreme process like heat to protect itself.   The evidence is literally in all of the manuals made by the companies that produce the guns.  Not a criticism, if your process works for you go for it but I dont know of a company that recommends something like that for basic maintenance.

It is a 'one off' on new guns.

It rarely needs to be repeated.

It is NOT a "maintenance" thing, but an initial cleaning and conditioning of the surface.

The manuals almost always make a quick mention about "cleaning and lubricating" new guns.

The grease they are shipped with is to prevent damage in long term storage.
It is NOT intended to be as 'functional lubricant.'

This gun has thousands of rounds through it, after each range trip it is disasembled cleaned oiled and put in the safe.  Out of 33 pistols this is the only one with a rusty trigger.   It isn't a new gun and I certainly don't count the grease or oil that comes on a gun to be lubricant

Heat the trigger and immerse it in BreakFree CLP and let it cool.
It sounds like you do not have an adequate oil film on the trigger.

You can use either FrogLube Paste, or any good automotive car polish with Carnauba wax in it.  This sort of protection should be good for up to 3 months' time.

I would clean it well then degrease it, then paint it black to seal it and move on.

Well Woody rest assured you're not alone with having a rusty trigger on your 365, I'm must be in the same boat as you, lol.  The easy fix was mentioned, lightly sand to remove the rust or dip it evapo-rust or both, degrease it and paint it with cerakote or norrels and moving on.