Bill, Dale has some good advice. Actually, you can't get inside the rear speaker enclosures (ie, between the mount and the grill), unlike the front speakers. The rear grills are not removable. If you're mounting a speaker, the screws pass through the speaker flange and into the nuts already present (if I remember correctly). The speaker "hangs" from the mount. Not a good description, but the best I can come up with right now.
Hope this helps,
Arthur
'03 candy orange
VA3BIT