I decided to apply another thick layer of Celuclay (the instant paper mache) to what I already had, and I made sure the top of the platform would be nice and thick. I plan on carving a big Tau symbol into it and I want to carve the rest of the platform to look like it is several sheets of metal fitted together.
The Second Layer 
Since this layer is pretty thick I'm giving it another day or two to dry before I sand it smooth and start carving. But, wait! Remember we still have two more cardboard circles to incorporate? That's going to be the roof of the firing platform. Let's cut up the plastic coat hanger to make some supports for the roof.
Coat hanger Bits 
After the coathanger got carved up I ended up with five straight bits 3 1/8" long that I'm going to use for supports for the roof, two candy cane shaped bits that will become fireman poles for bailing off the platform if it comes under fire, or a ladder, and a few other nice shapes that might turn into an antenna or something like that.
We want the roof to be detachable for easy model placement. So we will first attach the supports to the roof by poking holes in the cardboard to hold them. Then we'll apply a thick layer of Celuclay to the roof which should keep those supports in place. Finally we'll drill some holes in the top of the platform for the supports to sit in.
More pictures and updates coming soon