I have some stuff I'm gonna put into storage indefinitely meaning for at least a year and maybe ten or more. I know what to do with metal parts to keep them from rusting, but what about polymer?

Examples: spare pmags and other mags I'm keeping in case my daily use ones ever break. AR uppers and lowers I'm not currently using but might one day. Handguns that I don't shoot much but don't want to get rid of just yet. All these have polymer parts/furniture. Part of this is I'm in a ban state so reluctant to sell anything I can't rebuy.

Specific questions:

Is the grease and other chemicals used to protect metal safe on polymer long term?

What causes polymer to degrade? Over how long?

Does putting them in vacuum sealed bags help? Or is it unnecessary?

Anything else that does help?

Thanks

Avoid prolonged excessive exposure to solvents and oils (if they soak into the polymer, they can weaken it)
Keep them out of sunlight as UV light chews up plastic.

Judging by the Remington Nylon rifles I have had experience with it is not a problem.  Some of them are over 60 years old.

I wouldn’t store polymer in direct sunlight for years at a time, but it would probably survive that.

Common gun lubes shouldn’t bother modern polymers, but I wouldn’t store one in a tank of gasoline.

Just not a problem in my experience.

Vac sealed steaks last longer.

You want to keep them cool, in the dark, and not under tension or stress.

Keep the moisture content low. Many plastics can absorb moisture over time and this can cause swelling, distortions, and fractures.

So if possible I should detach the polymer parts from the metal parts and store them separately, so that the grease on the metal parts doesn't soak on the polymer.

Otherwise cool, dry and dark

That's the main thing I wanted to know. Otherwise I'd slather the grease over the metal and no doubt some would get on the polymer.

UV, heat and solvents are the enemy of all plastics. Some formulas are better than others for resistance to these.

Generally, keep plastic items in their original packaging. In addition, pack them into sturdy boxes. I use the $10 big plastic totes from COSTCO. Keep the top on tight. Store in a climate controlled environment if at all possible. If not possible, store them away from sunlight, heat sources and strong chemicals like fuels, oxidizers or household cleaning chemicals.

Iv’e got Glocks from the 90s that are still like new. Original PMAGs from (2008?) that are still running strong. One the other hand. I had the plastic parts from a 1970s Stevens shotgun literally crumble in my hands when I dug it out of the back of the safe. Again, different formulas.