Grand Trunk Hammock Compatible Sleeping Bag Sleeping Bag is a brilliant solution for hammock sleeping on cool and cold nights. Most sleeping bags compress under your back when you lay in a hammock, which crushes the insulating loft and lets your back freeze. But Grand Trunks Hammock-Compatible Bag wraps around you and the hammock, creating a warm, swinging nest. Hanging in the cool mountain air never felt so good.