Sleeping Pad As Gear Sling On Pack

Hmmm, on first thought my concern would be that the thermarest would be too wide without folding making the pack body either too wide or too deep to carry well.

Also why do you want to use the thermarest as a sling? I'm not seeing any apparent benefit to the standard methods of rolling or folding a sleeping pad and putting it in your pack. If you're using an inflatable TaR it also exposes the pad to more puncture risk (obviously a CCF is durable enough to ignore this issue).

I think implementation and field use may be simpler just making a bag out of lighter fabrics and packing the pad in your preferred method.

If there is a specific reason that you want to use it as a gear sling that I'm missing let us know. I just think any cover you make to keep the pad in a U shape will be pretty much the same weight as a standard bag anyway but with a lot more hassle to construct and pack.

I too am working on such a project, however one extra item. I wanted to be able to ditch the frame and use the U shape as a soft frame. I'm still working on how to make the shoulder straps sturdy yet detachable so they can be put on the external frame. I've made two packs similar to what you speak of, but without the ability to be attached to an external frame. Some inspiration can be found on the moonbow website, as well as the luxury lite site. Ula epic comes to mind as well. Also check out the granite gear flat bed and molle mac pack.
Hope this helps.
Joel

I think my thoughts behind it were that if I am going to carry it, why not see if I can make it accomplish something. Copying Kifaru’s idea of a cargo panel,
http://www.kifaru.net/cargopanel.html
I can stuff a jacket in there, carry awkwardly shaped things, etc. As a rolled up tube, that's all it is. And I could also unclip it, and sit on it at rest stops. I may look into CCF instead of a TaR. A TaR is what I currently have, but CCF I could make narrower.