I can usually roll my 3/4 thermarest up so it snugs inside somewhere. The CCF pad is more difficult. I usually end up leaving it out. But I can imagine different geometries inside the boat. My Mariner doesn't have bulkheads (old school, the designer didn't believe it them). So it is easy to pack because I don't have fit bags down a hatch. I tried have the pad form to the inside circumference but it was so "sticky" that it was difficult to slide other bags past it.
But more to the matter - it seems thermarest style inflatables have a large advantage on insulation factor - which is why I'd use a pad in a hammock. I really don't need it to soften the ground.
Brandon didn't give me a Max width for the BlackBird. He just said 20-25 inches (most common widths) would work there an maybe a pinch under 30 inches for the Ridge Runner.
When I use the Hennessy with the undercover, there is no issue at all because I am not trying to fit a sleeve.
The sleeve is also my concern with the wings device. I got a BB double because I figure the pad would be less hassle and stay put better in a sleeve.
In the past, I've used a thermarest in the Hennessy undercover and was never cold - admittedly also in warmer summer. I tried a CCF pad in the BB and could feel a little chill.
Unfortunately - it is sort of a race now. Each day the nights are getting colder so the comparisons aren't fair.
I have a Really Wide thermarest that I use for car camping. No way I can fit that in the boat (and I don't want to fit it "on" the boat). So I'm in the market for something better than my 3/4 length old "guide" model.