Long term mold storage?

[Outpost75]

Pure mineral oil USP from the pharmacy gives good rust protection and sublimes away easily and completely when blocks are pre-heated on a hot plate, leaving no residue.

[FISH4BUGS]

This may be declared heresy, but when cooled down, I spray my beloved Hensley & Gibbs moulds with WD40....yes, WD40.
Then I tightly wrap the mould in a plastic bag (like the ones you get at the supermarket) and tape it shut tight around the handles and mark what mould it is on the tape.
The handles stick out of the bag, and there is no need to protect them.
I do 2000 bullets at a time and sometimes, like the OP, I won't get back to the mould for a year or more.
They are stored in an unheated (unless being used) but somewhat finished casting and reloading area in the barn (used to be a horse stall).
It is subject to heat, humidity and -20 in the winter.
I have NEVER had a spot of rust.
Cleaning before using is break cleaner, rag and QTips.
I have been doing it this way since I began casting some 40 years ago.
Works for me.

[atr]

I leave the mold full with last casting, then spray outside with WD40 and then wrap it in an old cotton sock. Never had a problem with rust. Some of my molds don't get used for a year or longer.