I would never vacuum seal my cannabis. First off you're going to end up with mold. Cannabis shold be fairly dry when stored, but not crispy. Sealing it up with no air works well, but the act of vacuum sealing flowers will crush your precious flowers and knock valued trich's from the plant. When I do long term storage, I keep it in jars, in a cool dark spot. I still try to open those jars once every couple of weeks, cause they will still mold in the jar. If you are sure that your plant is completely dry, you can get a vacuum sealer for jars. I still don't recommend it tho.
Peace...j.b.