>How do you carry the Gossamer Gear ThinLight 1/8" full-length sleeping pad?
I roll it up and lay it, U-shaped, in the bottom of my Mariposa Plus pack. It holds the bottom fabric out, then my stuffed quilt fits inside the U. That make a nice base for efficiently filling the rest of the pack.
>You think the torso + thinlight would work ok with a Zpacks Z1
I think so. The torso (I'm assuming you mean the GG NightLight torso pad, not the BMW Torsolite which stores in a stuff sack) is 10" x 18" x 2.5" when folded and makes a sturdy packframe when you stuff the rest of your gear against it (since the Z1 doesn't have a pad sleeve). It will also keep hard gear from poking you in the back, and keep your gear from getting wet if you soak through the back of the pack. It certainly fits inside the Z1, which is 12.5" x 30" x 5.5". (The Z1 looks like a really nice pack! I need to reduce my three-season gear volume first, though.)
A rolled 1/8" regular-size ThinLight is a cylinder 20" long by 3.5" in diameter. (PJ, that is diameter not radius ;) You can bend it in half to make a 9" x 6" x 4" object that you can place into the bottom of your pack. (It should just fit in the bottom of a Z1.) Alternatively, you could bend it in a U-shape and place it inverted in the pack to give the pack a good shape and to hold the NightLight torso in place while you fill the pack. Finally, you could unroll it around the inside of the pack and fill inside it, but the pad is likely to lose a battle with a tent pole or other pointy object eventually. The ThinLight 1/8" pad isn't fragile, though; mine shows no sign of wear after about 30 nights, including inside a hammock where it was subjected to severe stretching (conditions that tore a sunshade to shreds).