I have since made some triangle "thingys" to help with suspensions sag by morning. Mine is a side zip, so I'm not certain if the triangles will make it more difficult to enter from the bottom. The Potomac fits the Expedition like a glove.
Just tighten up the shock cords till she's snug. Don't over tighten the ends, your body weight will tend to close up a bit of a gap there.