Looking to get some cold packs for shipping over the next couple of months. I know ideally Phase 22 is probably the best choice. But to cut down cost to the consumer both for packs and shipping cost I'm looking at the dry gel packs. Anybody use those? I'm looking on TSK's site and can't find how long they stay cold, that's my only concern. Looking for at least 48 hours cooling, but with styro lined boxes they should stay cool longer than if they weren't lined. Thanks in advance!