3 months in the freezer in a plastic bag with a desiccant pack should be okay.
Honestly I'm not so sure you should go through all of those "cleanses" before starting on low doses--12mg or less.
The Liver Cleanses
typically are the most troublesome to some members of chelation groups. The cleanse might work fine for fairly healthy people who want a little "tune-up" but there have been many unpleasant reports from those who have liver problems.
Milk thistle seems to be fairly well tolerated in the HM groups.
Low, frequent dose oral DMPS is generally better tolerated in the early months than DMSA by those who are too sick to work.