squishy cellulose insulation. After considering, foam glass, Skamol, sawdust, and Perlite, I decided to break down the oven (took 10 minutes) and build a 2x4 matrix in the oven base and refill it with the cellulose. My woodworker, insulation guru told me I should not be so quick to give up on the cellulose. After reassembling the oven, it really is looking much better. I believe I've solved the squishy cellulose issue with the matrix.
Tonight I will ponder the sleight sidewall height differential regarding the brick and solid block, and then on to the oven roof.