The next consideration was the tube diameter. I picked a diameter in the multimode-bordering area of a Fresnel number of around 2.0. Anything narrower would waste quite a bit of the beam and I didn't have a need for single-mode operation. It also helps with heat diffusion and a tiny bit with expected power output.
Finally I picked a cooling jacket that just looked about right... I am relying somewhat on the thick wall of the cooling jacket (.157") to provide some structural stability to the whole thing. A little weight isn't necessarily a bad thing here.
I know everyone is clamoring about the mirror mounts and beam folder assembly -- or at least I imagine you do. More is in the optical resonator section.