How much BP is too much? and temp storage ?

I don't store this in the house, but rather the MIL house out back due to the fact that we have lightening storms (and perhaps if its struck, maybe the MIL might actually be visiting? Ok, I kid...)

This MIL shack is well insulated. One half is a storage area for lawn tractor and gardening stuff.
Temps vary between a max of 80 deg in summer and about 25 deg lowest in winter here in NW MT.

What is the shelf life on this BP at those temp ranges?

[Linked Image from photos.smugmug.com]

To be blunt , longer than any of us

SD60, each adult in the residence is allowed 50 lbs [two cases] of black powder, as jmd025 said, it'll outlive all of us.