fyo since you used the xtc baffles 1/2" mdf will work best adn all you need is a ring no more than 1" in width ie.. if your cutout is 5" the ring total diameter should be no more than 6"--make sense I hope
good deal on the final install
also cu the back out of the xtc so the mid can have more air volume to work with instead of a small cup--infinite baffel speakers need air to work with as much as possible