DIY vacuum former for sheet plastic

Single vacuum motor, with second stage deep vacuum check-valve.  I staple the plastic to a wood frame that fits in a toaster oven.  325 degrees seems to work well with HDPE, PET plastic (2-liter bottle) seems to shrink too much to be useful here.
vacuum formertwo stage vacuum valve
mold and thermoformer negativevacuum former frame for toaster ovensheet was heated too hot, developed holes, plus I gave it a '"hickie" in the center of the wrench