I liked the top video best...I found this info at HPA regarding vacuforming/thermalforming:

"Perhaps a few hints about thermoforming might help.

First thing is to bring the inside volume of the box to a minimum to avoid having to extract to much useless air volume. As the box itself has to be at least 2-3" of height to make the hole for the vacuum cleaners hose, fill the inside volume with a piece of expanded polystyrene. On my one I just left 2cm in front of the hole's opening and 1cm between the cover and the polystyrene. So air volume to extract is to a minimum and it draws down the plastic sheet faster.

One other trick which helps a lot (and cannot be used on real thermoforming machines) is, once pulled down the sheet, leave on the cleaner and reheat the sheet with the hairdryer on the sides it did not adhere to the plug. The vacuum from the cleaner will slowly pull the sheet against the plug in most places. With acetate sheets you can get mouldings with complex shapes you would never have dreamed off. You can even smooth out wrinkles in the edges."
Urs

Here are a couple of You tube links for similar items, that seem to work a bit better.

https://www.youtube.com/watch?v=uMbX3bqfzsk

https://www.youtube.com/watch?v=2BR9aayq-tw&nohtml5=False  by the way if he had sealed it better he would have been able to use only one vacuum.

I find it great to make wind screens, cowls, engines, and such that you will make several of them over time.