Hi.
There are many Different ways to make an under skull.
One is using a vacuum forming machine which allot of us Don't have..
But,, there is another way to make one.
When you cast the GEL-10 into your mould, Get the Right thickness of layers you want & Let it cure Completely.
Then you can use Easy-Flo 120 Directly into the mould Behind the GEL-10 Skin, make sure it does not get on the Ultracal mould.
you need to Slosh it around the back of the Silicone you want to
Make an under-skull For, until it Go's Solid White..(5-10mins)
I would apply 1-3 coats until you have a strong thickness..
When it's Fully Cured (30-60mins) you will have A Solid under-skull.
when you remove the Two half's of your stone mould,
you can pull the whole Cast out together and Pull the GEL-10 off the under-skull Like A glove mould.
This will also keep the GEL-10 in its Original Sculpted Form when fitted to the Under-Skull..
Now You can start to figure out which parts of the Raptor you want to move with Servos or Pull cables..
you can use more GEL-10 to bond the cables & Resin as GEL-10 Will stick to GEL-10 Very Well.
I would look at Buying A Good R/C Transmitter which has 6-8 channels if you plan on building An Animatronic Head..
I would suggest Looking at Many you tube clips on Different ways to get the Movement you want.
Many Animatronic Experts Do Not show you any of there Tricks on building there Creations as they have spent many Hours
Finding there own ways to Get them Right.
The best one available is At SWSCA And its a Puma Tutorial 6 hours long.:eek
Hope this Helps. :thumbsup