In a ute you ask...
Just thought I'd give my 2 cents help to anyone out there wanting to put a bigger sound system in a ute, basing from a XF (being very little room).
After some persuasion (friends sister always crankin her sub) i thought to myself, "i wanna sub". but where to put it. so i went to see the guy down at the local autobarn and had a looooong (as in long, they closed the store around us talking long) chat about what he had seen and done. turns out that behind the driver side seat, in the lower section of the firewall there is a hollow space. A 12" sub will fit snugly into this area. behind the passenger seat is the fuel tank, and as i now run on straight gas (mounted in the front of the tray) im thinking of removing the tank and installing another 12"(scary, 2 12" subs in a small confined space).
As for 6" (i went for splits), they can be mounted in the door, as there is a space provided for this in the front bottom corner of the door, but i didnt take much liking to rattling the doors away, and have made up some custom kick pannels to fit the 6". and as for the splits i have located them approx 1/2 way up the front pillars.
Hope this helps out a bit, and if anyone has any questions i am happy to try and help.
XF Ute. 351. LSD 9" 4wdics. Manual. Lowered. Tinted. All Elec. 16" mags. Huge "doof doof".