I keep the containers for conicals. They are crap for keeping t7 long term. Keep yer t7 in any kind of sealed container with a dessicant pack in there.
When I first got into muzzleloading a few years ago, I started with 777 pellets. I was completely ignorant of what proper care was needed for the pellets. I purchased a pack in January of that year and by October they were worthless (with no care taken to protect from moisture...I live in NW PA). By all means, vacuum seal those suckers!