There are DVD and bluerays designed for long term storage, if are are willing to spend the money.

M-Discs are not cheap, but durable- Best buy by me carries a 5 pack of 4.7 Gb MDisc for 11.99

They make 4.7 Gb
25 Gb Blueray
50 GB Blueray
100 GB blueray.

You just need to have a DVD/Blueray in or near your machine...