I'm sure you have your reasons for wanting this, but the retail packing it comes in is really quite adequate for the job. Its very light, can be closed again, etc...
I had a bad experience this weekend with the container that comes with the heat sheet. The package got turned in such a fashion that the sharp corner was pushing against the fabric of my backpack, and the corner poked a hole through the fabric of the pack.

I threw the container that comes with the heat sheet in the trash the second I got home. I think this is a very salient thread!