We've had this 'what the life expectancy' thing from you in your 'cartridge' thread.
What with the obsession? Things wear out. No point in worrying about it - deal with it when it happens. It's far easier to address the issues that age creates than to try to alleviate it as an ongoing problem.
Either use it (and expect wear) or don't.
CRT's are obsolete - get used to the fact as there will be no spare tubes around in the future (too expensive to manufacture/store) so look to alternative technology to replace any CRT device you may be using 'now'.
If you want to store things for potential resale in a future marketplace that commands high prices for vintage technology then look at the manufacturers storage instructions. These will be found in the technical documentation that they supply for the CRTs themselves (data sheet).