Joseph – I think you are
Joseph – I think you are over complicating the solution
All you need for the dams is an old cut up kiln shelf and some fiber paper (thicker is better).
Here’s a picture of the setup as viewed from above:
Not shown is that you want a piece of fiber paper under the whole setup. The result is that the fibre paper works as a gasket of sorts between the kiln shelf slices (or other appropriate kiln furniture).
To reinforce the sides, simply put something with heft against the dams. Additional pieces of a cut-up kiln shelf works great.
I’ve used this setup countless times, including for 2″ thick paperweights. Done right it never fails.
Helios Kiln Glass Studio