Step 1: Create the mold - 1
Then, you must create a mold layout. With the masking plate down, I laid out all of my mini figs. They will shake around a little bit from the platform going down and up. I might try attaching them to a large, flat lego surface, but you must be careful to not cover the vacuum intake. It worked pretty well without that, though. Keep them away from the edge by about an inch.
Then, lower the tray. Since they are plastic, I lowered it quite a bit to make sure that I didn't melt them.
Step 2: Create the Mold - 2
!! Do not use a plastic that is toxic!! PETG is a food grade plastic, and it will not poison you when you make chocolates.
Make sure that the clamps are set before moving on.
Step 3: Creating the Mold - 3
If you wait too little, then the plastic will not be pliable enough, and the mold will not get into the nooks of the pieces. You can still use that piece of plastic as long as you don't have holes in it. Just reset your pieces and start over.