Storing proof base metal coins.

I have a collection of GB proof year sets with lots of duplicates. Some have terrible toning, some look like they have just come out of the mint. Some years seem to be worse than others, and some like the 1970 set never ever seem to tarnish. What is the best way to keep them so the coins stay “FDC” ?

Like most things that are stored long time, in a stable environment. For coins; the lower the humidity the better, temperature as stable as possible (no high fluctuation like in an attic), no smoking or other high sulphur exposure (obviously the less handling the better) and for silver keep them out of the light to avoid photo-oxidation.