Out of curiosity, would there not also be a risk of the amplifier interfering with the circuitry of the Carputer? Just thinking about the kind of power passing through the amp's board when powering subwoofers. Also I'd be concerned about running the amp and car pc off the same power cabling into the case; I'd imagine the voltage drop across the cable would put strain on the carputer's PSU. Again, for subwoofers, you might need one of the nifty wide input PSUs for peace of mind.
It would be absolutely awesome though
and as far as sticking bits of amp in a case goes, perfectly feasible so long as you can sufficiently heatsink all the neccessities.