Vacuum forming even complex objects is extremely simple!
The video below shows a complex robot face duplicated in seconds.
To make your own vacuum forming table, begin by measuring the inside of your oven.
Next, make a square wooden frame that will fit easily in your oven space.
 

(The frame must be at least 2.5" tall to allow the plastic to "slump" when  heated.)

Build a simple sealed box in the same dimentions.

The top of the box should be made from common perfboard, and a section of tubing should be inserted through the side to connect to a Shop Vac.
Use Goop brand glue, or silicone to seal all seams and the hose fitting.

To use your vacuuformer:

Place the item to be copied on the perfboard side of your vacuum box.
Staple a sheet of polystyrene plastice across your wooden frame.
Set your oven to 400 degrees.
Heat your frame until the plastic sheet slumps about 2 inches.
Quickly turn on your vacuume, and cover the piece to be molded as seen in the video.
Make certain your frame makes a good seal all the way around the object to be molded.
Let the magic commence!