I have never seen a 13lt Dromedary bag but I have several 10lt ones that I use on long trips.
One is SECURED to the bottom of the cockpit, just in front of the seat (behind the seat I place smaller items since a 10lt bag doesn't fit).
Securing the bag is imperative for me in case of a capsize. I have made 4 sturdy small saddles (from fibraglass) and epoxy glued them to the hull, inside the cockpit. Details with images here: http://gnarlydognews.blogspot.com.au/2009/07/shop-underdeck-storage.html
1 Canoe/Kayak Trailer
Full Size Sail Rig
4-place Boat Trailer
Pull-Up Strap Handle Kit
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