Because the mannequin head is hollow, we will need to fill it in with something to dampen any reverberation or resonance. Since this is a tutorial for the budget minded people like myself, I propose using old t-shirts to fill in the "brains" of your dummy head. I've found that this works well to mitigate any problems associated with hollowness. If you have a torso or partial torso, fill in that area as well.

Some people will go so far as to fill the head with a jelly sack (maybe a silicone implant ;-) to simulate a liquid-ish brain. Feel free to experiment with various materials and let me know what you prefer.

Just remember that our ear canals stick out inside the head and care should be taken to avoid pulling or putting stress on those canals. T-shirts are cheap and easy to work with.

Run the mic cables out of the head either through the bottom, or through some other hole.

If you carefully cut out the access hole, you can re-seal the hole using the cut out piece. Otherwise, it's not likely going to affect the performance, so you can just cover it up with a wig.

I'm partial to the British cut...

Next up, get ready to calibrate and test the head.