Ok heres the reality of your situation. You are going to be using something like 3/16th inch thick ABS to make the molds. This isn't going to pull down with a vacuum cleaner. You will need a vac pump/tank/valve as well as a heater that can get the abs to temp without charring the surface. The open ovens here have a drawback in that they heat from the bottom, and as the material sags, the center gets a disproportionate amount of energy. I have a 2 x 2 oven box with a 220 oven/broiler element in it. 3/4 plywood faced with hardiboard. It is 12 inches tall. I run it wide open/full power and use the distance to prevent overheating. I run bottom heat and run 3/16th abs manually with decent results. Heat times are around 90 seconds and i have a metal pie plate on the center of the element to reduce center heat soaking. The center of the sheet is about 15 degrees hotter than the corners. For a simple frame, use 1/2 x 1 furring strips on end and make a frame. Cheap gate handles make it easier to lift off the oven. I use a 5 cfm robinaire pump pulling on a 25 gallon propane tank (the old heavy ones) with a McMaster Carr p/n 4625k63 with the squeeze lever arm to run the vacuum on a foot pedal. put a T on the tank, one side to pump, one side to the valve. The other side of the valve to the plenum box. Simple, cheap, effective. Hard to go wrong. Ask more questions and I'll try to aim you a bit better............ Scott.