I minimize the super-compressed sleeping bag by wrapping the bag around my rolled up tent (in its own sac for those days the tent doesn't dry out enough), and then stuffing the whole thing into a dry sac, which I then strap to the top rear rack with polypropelene webbing. I cinch it tight enough to eliminate all wobble. The trick is to leave a tiny bit of air in the dry sac when you close it so that when you cinch it super-tight you're biting into air rather than into your sleeping bag. Make sure the dry sac is a durable one.