I blogged about these PackMate bags a few weeks ago and to date they seem to be working well. The bags are designed to hold clothing for long term storage and are quite robust with a grid 'mesh' and an apparently sturdy zip lock. 
Parachute flares fit exactly across the width of the bag, which means it can easily be rolled.
It fits into a much smaller space than a dry bag and slips into a bungee behind my seat in the kayak cockpit. I've only used them once on the wate and will report back on their longer term suitability.