I'm in the process of getting this T-Rex bust (from Prop-Builder) ready for paint. It arrived in four pieces: head, tongue (both foam filled), and upper and lower jaw.
Size comparison to a Predator Bio Helmet:
First task: cut the lower jaw off with a dremel and then remove all the foam from the head. The saw was inserted in the Rex's jugular for dramatic purposes, and then used to remove the majority of the foam from the inside.
Test fitting the jaw with the teeth inserted:
I then used plumbers epoxy to set the lower jaw back onto the bust. It said it would set in 20 minutes, but I ended up holding the jaw in place for 2 hours while it hardened haha!
Then I used Apoxie Sculpt (love this stuff!) to fill in the gaps and create the membrane inside the mouth. As it dried, I textured the skin.
Now it's ready for another coat of primer and then paint!