bi-amping and xover?

Timely, yes, right now.  I'm on duty ;)

Both of those JL amps will have good steep crossovers built in.  I would leave the head unit at flat (or full range) out and use the LP and HP crossovers on the amps.  Use a test tone CD for some incremental tones in the range of around 80 Hz up to about 100 Hz.  By listening, tweak the LP for the sub so that it starts to fall at 80 Hz.  Use the HP for the mids and adjust so that the tones start to fall off BEFORE 80 Hz.  Once done, you will have a 80 Hz crossover point.  Slight tweaking after some listening is usually needed to get it just right.  And you may want to adjust both crossover points up a little bit in Hz if the mids are sounding a bit strained at 80 Hz. 

I like to turn the volume down while adjusting crossovers.  It lets your ear be more aware (not in defense mode!) and is easier to hear when the volume drops off.  Make sure all damping is done and gains are readjusted on the amps before this final setup is done.

The MDF baffle:  measure to see what space you have.  You can use regular 3/4" or you can use plywood that is 5/8".  You could also rout out the perimeter of the mounting hole so that the woofer sits flush with the surface if front room is too close.  Cut the baffle size so that it fits the door, no matter what shape that would be.  Apply caulk to the back where it contacts the door panel and then screw it in place.  Caulk all around it once it's installed.

The mounting baffle in this pic was once the top of a put-it-together shelf unit, which is why the surface is painted white.  I flush-mounted the woofer by using a router.  It is screwd into the panel with sheet metal screws and caulked.  I doesn't matter what the shape of the baffle is as long as it fits the confines of the door's contours.

stevdart,

here is a link to pics of my truck so you can see what i'm working with.  it will give you a good idea of where all my mounting points are.

http://www.cardomain.com/id/holty