I think my bag at the edges where it is next to a tube is roughly 2 inches, but when you pack it fuller, it gets thicker. I would guess that the thickest point on my bag is 3.5 inches in the middle where I crammed it fuller.

My bag is slightly smaller than full triangle, in the photo you can see I can put one water bottle in the frame. It is the large size Ibera that I got on Ebay for about $15. Also, I added straps to the head tube and downtube, I am not using the strap that came on it to the seat tube. I am guessing it is about 5 liters in volume.



You might get better luck getting answers for home made bag at this site:
DIY / Make Your Own Gear (MYOG)

I leave tomarrow for my first trip where I am using the bag, ask me in a couple weeks how it worked.