memphis shallow mounts in suv

I just bought an Expedition, and I am considering building a subwoofer enclosure in the inside rear quarter panels in the back in order to save the cargo space (so, pull panels, fiberglass up an enclosure, etc etc). I already have a Zapco 9.0 that came out of my former car, so I'm looking at pushing 2000 watts when I turn it up (yes, I know of the electrical requirements, etc). So the idea was to install two of the 12" Memphis shallow mounts on either side facing directly across. I am afraid that frequency cancellation will take place. Any thoughts? If I need to, I guess I could angle the subs to the rear a bit more. Also, anyone done this? Also, anyone know what the recommended enclosure size is for these subs? I can't find anything online. Thanks.

The only time I would use any shallow mount sub would be in a standard cab pickup truck.  If you have room for a conventional sub, use one.

That's a possibility, but even so, the question about cancellation still remains. :)

4-5 ft across and sealevel. ;)

Ithere will be no problems with cancellation.  At sea level a 45Hz waveform is 25 feet in length.  Both speakers will be relatively the same distance from your spot.