bought my twotone 84GL with a nice Sony 10disc changer and two pairs
of ~6" speaks already installed.  This is nice because i like
listening to music in my van.

I've no knowledge of how to do stereo improvements, but ive thought
about upgrades since the beginning.  Today at lunch my friend offered
to sell me his alpine amp and a 12" Phoenix Gold sub mounted in a
sealed wooden box.  We looked and it appears that it would fit nicely
under the first row of passenger seating, which i have turned around
facing backwards to the second row, conference style.

blah blah searching the archives blah blah, but does anyone have any
important nuggets of info pertaining to sub install specifically, e.g.
this brand of speaker, what the addition of a 12" sub will sound like,
if there are helpful changes to the smaller speaker setup that are
worthwhile to balance the sound, and tricks/traps to placing and
mounting amps and subs in a passenger van.

Thanks in advance/  sp