If the sharp edge problem can be solved, I think we just found the ultimate pack-flat PSK water boiling container:

They make stainless steel pouches for heat treating. The smallest I found was 2.5" x 5"

http://www.mcmaster.com/#catalog/115/3685/=3mnd9u
Very bottom of the page.

You could fold it in half or cut it shorter. Perhaps some high-temp silicone tape over the edges.
_________________________
- Tom S.

"Never trust and engineer who doesn't carry a pocketknife."