Oh yeah, a possibles bag. I like the idea. You can waterproof leather fairly well these days.
A lot of people these days think a possibles bag was what muzzleloaders kept their reloading supplies in. Not so. A possibles bag was the original psk/bob. Old timers kept a lot of important stuff in there, like firestarting tools, food(pemmican), letters from home, and yes, also sometimes a separately packed reloading kit and tools.
Leather is more resistant to fire than nylon, and holds up to UV better too. I like leather.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)