Put it inside garbage bags and strap it with the bungees on your rack. No reason to make it complicated especially since you'll leave tomorrow. Double bag the sleeping bag if the compression bag is not water proofed. Take an extra bag in case one rips.
Have fun on your tour.
BTW, in this picture I have a 20 degree sleeping bag in the front bag (packed in a compression bag) and the tent and sleeping bag in the garbage back on the rear rack. This was for a weekend trip.
http://2.bp.blogspot.com/-k7hkr23ynl...-35-45_144.jpg
With a bigger bike and more bags I put everything into panniers.
http://1.bp.blogspot.com/_eJrHDMPMpy...rward+east.jpg
http://4.bp.blogspot.com/_eJrHDMPMpy...ical+site2.jpg