"I have never used OPsacks before but I am thinking I should on the A.T."
Before you commit to using the expensive OPsacks, you might want to investigate the Nylobarrier sacks sold by Lite Trails. They are made entirely of the odorproof material that is laminated to a thicker non odorproof layer in OPsacks. They are much lighter, .4 oz, for a larger storage capacity, cheaper, quite durable, and a whole lot easier to use. I can use them for several trips if I don't outright abuse them. Simply turn them inside out, wash them, hang 'em up to dry, and they're ready for the next trip. It is wise, however, as with an OPsack, to check for leaks by sealing them up and applying pressure from time to time. They're light enough that I usually carry a spare or two in the field. Love 'em.