Second Tony's methods.
But I eventually found that I needed more room in my pack so I roll the Nightlight and Thinlight together on the outside and strap both to the side of my Jam2. I'd previously found that the Nightlight Torso was just shy of what I needed. So, I purchased a full length of the Nightlite, measured from my shoulders to just past my knees, cut, and then cut a panel off that. I put the panel in the pack, inside a garbage bag, for structural support.
BTW, if you have a pillow, like the Montbell, it'll stay perfectly in place with the Thinlight under it.