Pretty much identical to the one here http://www.thingiverse.com/thing:35402 except rectangular, with legs and a bent vacuum connection..
I also added more holes and grid lines to allow for more detailed molding

Print with at least 2 layers and an infill of about 20% or more. should print with out support.

glue the stand and the gasket and the base together. (Use hot glue or something to seal any gaps it needs to be air tight) place a rubber band around the poles of the stand. to allow for a better seal between the mounts and the stand when forming.

I used Magnets in the Plastic mounts to hold them together.. but you can use screws and bolts or you can hinge them together if you want.

use the Platstic template to draw the shape on the bottom of a plastic plate then cut that shape out of the plates.. these will be the plastic sheets you use with this machine.

you will need a pretty good vacuum to connect this too, I used my small house vac but it needed an adapter to fit the shop vac sized hole. so I included that too. (you may need to alter it to match your vacuum)

Also you will need a heat gun. tempreture is everything.. if the plastic sheets don't get hot enough.. the final mold will not have enought detail.

To use Vacuum Former: Turn on your vacuum,
Place the thing you want to make a mold of on the stand..
Then heat your plastic in the mounts.
when the plastic gets hot enough, press the mounts down on to the base and the vacuum will do the rest.