I went and got some steel angles to use as rails inside the oven. I then (with Tony's help), leveled them and screwed them in with self-tapping screws. This works pretty well so far and keeps the frame far enough above the heating element to not burn the plastic.

Here's the hand armor bucks getting ready to be vac formed.

A sheet in the frame ready to heat up.

And now...a little video of our first pull. I'm very impressed with how well these foam bucks stood up. I think we could get alot more pulls off of them if we wanted to. I think I'll keep them for backup bucks.

The first three pulls. We did one and then we couldn't stop. Shown below are the hand armor, shoulder bell and bicep (front & back). There's some issues with creases. Maybe the plastic is not hot enough or I'm not coming straight down on the mold. Some more experience with pulling will tell me more.