I've decided to go for a waterproof bag which would allow me to carry the bag on the top of the rack if needed and obviously I'm drawn towards an Ortleib, the PS 10 compression sac with a valve to allow trapped air out. Has any one used one of these as a stuff sac for a sleeping bag? Would moisture retention be a problem or should I go for something like an Exped sac or a Pod airstream compression sac.
Any help would be useful as I'll be needing it in about four months and there's no way I can decide this on such a limited time frame on my own