I have a table that I made that could do the job, the dimples may be moisture as that happened with my fencing neck on the first try.
You dont really need to vacuum form it if you have a thin enough piece of material. Some sort of colored polypropylene or something. Additionally you dont need a vac table per se'
Options....and I have done all of these with sucess.
1. Build a cheesy "vac table" for a small job as this. You can use a wooden TV tray with a hole drilled for the vacuum source. A regular house vacuum with a hose should do it. Lay your molds down and then with 2" masking tape, lay a piece of material over your molds making sure they overlap by 4 inches all around. Turn on the old heat gun and when it gets pliable turn on the vacuum.
2. The exact same as above except dont use a vacuum...wear leather gloves and press onto the mold as you go.
3. Cut your plastic to shape, heat it up lay it into the eyesocket of the mask and press an egg or your mold into it from the inside.
Eyes are simple but you'll need a few practice tries to get your rythm down. Hope this helps!
Example using option 2