For the third round I wanted to focus on correctly honing in the geometry and adding a strap across the body of the cup. I figured this could function as both a handle and as a way to lock the lid in place.
Unfortunately the first lid I made turned out pretty distorted. I'd picked a scaled design that I knew would distort the lid to some extent but I grossly underestimated by how much. I did make a second lid, sized to fit directly over the body. Of course, the geometry of the stitching meant that the lid is now exactly the radius of the body. I should've added 1/4" to the radius to account for that.
I don't really plan on ever selling these prototypes and I've got enough work at the moment so I think this one will remain lidless for the time being. I might use the lid from the Mark II to test the design elements but so far it all seems to work as a proof.