it's no secret i drive an mgf. at the end of the day - when i crash, i won't have bits of audio equipment crushing me.
Oh! Thats a shame!
If you have a three door, you can fit the amp, if its small enough, into the rear side panel, then just run the cables from there. Then you will only see the sub in the boot and that is easily removed in case you lay the car up for some reason. Then nothing is seen.
You would need to insulate the connections well though, in case of a side impact which could ground out the battery.