Rear Speaker Downsize Adapters

Does anybody have adapters that they have made my hand for a 6x9 to 6.5" conversion. I have a pair of Type-R components and I was thinking some thin wood, less than 1/4 inch, would be good and wont rattle like the plastic ones do. That might also give the woofer a more solid mount. If anyone has any ideas...Id appreciate it.

don't wanna go too thin on that wood, or it WILL vibrate