Hi Mike;
Nothing too fancy, just a little extra work to make it work.
I use a simple wood block about 1 1/2 inches thick and then I glue a piece of plywood to the bottom to strengthen it.
You can buy router bits in any size you need, rout the block of wood, I rout about a 10 inch grove in the block and this makes two ends where I can get two separate cases from each mold.
I glue a piece of formica to that and rout that out, this really helps to protect the top of the mold.
I make a matching piece to go inside the groove minus the thickness of leather, the last one was made with clay that can be hardened in the oven.
Use a piece of plywood on top to press on.
Cut a square piece of leather, soak it for twenty seconds, work it into the groove and then put it in the press for a couple of hours then take the mold with the leather and put it in the oven to harden it.