Keptin, there be 4 x 6's in the Kick Panels.....
I took 2 of the small drywall mud containers, and cut them down to both fit the contours of the kick panels and be as shallow as possible to fit the speakers.
Cut a hole in the 'bottom' of the container and fastened the speaker.
When I cut the container I left tabs on 4 sides, reinforced with small metal 90* brackets. One goes over the top of the kickpanel, the other 3 I cut slots in the kickpanel, riveted together, carpeted.
All done with stuff I had, including speakers.
You can see them in pic. No, I don't actually kick them, but the vent doors don't open completely.