Three M6 stainless bolts with nylock nuts hold them in place (two to a-pillar area, and one through firewall). Also they are an "interference fit" which means I have made them very snug (hard to get them in!) so they'll be nice and secure.
Marked out filler panel for the sub box....
...so I knew how far to apply the filler to provide further strength and to smooth out the bumps.
Bolted in the drivers side kick panel this evening - certainly isn't going to rattle as it is tight to get in and the three bolts with nylock nuts make them very secure.
Fortunately managed to run the speaker wiring fairly discretely. Tomorrow the passenger side will go in.
