I'm not convinced on any design for the bottom of the foundry, so I've been musing over some different options 3d models to come) the first is to buy some fire bricks, then mount and skin them with refractory cement.
Option, the second, is to mix up a batch of TKOR Refractory lining, then skin with refractory cement, This option is definitely cheaper, but i;m not sure i'll get the life i desire out of the refractory skin with this style of underlayment.
Option three, is to have a puck of some kind of masonry in the middle, with a surrounding of ceramic blanket, possibly with a sacrificial steel plate to catch any spills. i;m not sure i like this idea at all, but it's here...
Option four is to have just the bed of Ceramic Blanket and hope the crucible doesn't tip over. could wire in a ring of material to act as a "nest" for it, but I fear that will lead to too much differential heating that it may lead to crucible damage.
I still have to mull over this, and re-import my materials library, so I can actually start coloring these models. Eventually I'll go back and re-color the old sketches, but at least it'll still get the point across.