well, I've tried the NeoAir full length pad, the Z-Rest pad in combination with a torso-length Therm-A-Rest, and even the wally world blue pad cut to fit, and nothing eliminates the gap in the Blackbird, so...going for the underquilt!

The first night was an unmitigated disaster! There i was, watching the stars twinkle, the moon out glowing in the darkness while occasional clouds passed overhead. I got to listen to the breeze sighing in the Ponderosa Pines, making that moving whispering sound; an owl or two calling to it's make, and the coyote party animals a few ridges over, apparently enjoying a kegger! It was fantastic, and I was like a 10-year old, loving every minute and waaaay to excited to close my eyes. then I realized it was 0230, and I needed to get up at 0500!!!