Using a android tablet embeded in my car I want to replace mycar hifi with a tablet, I have worked out the mechanical issues with putting a 7" tablet behind the dashboard where my exisiting doubld din car ICE is, with it behind the trim i have no access to volume or power without removing it, is there a device I can get that can remote control the volume level and/or the power on/power off functionality.
The tablet will be connected to my amp for final audio output.

cheers for any suggestions (thinking of hacking a BTkeyboard to bits for button funcion unless you can recomned somit better)
How about using widgets? Probably cheaper and would let you control all the functionality on the device itself, without any external hacks.

For volume control, you might be able to do with a widget similar to Volume Control Widget and for the power menu try an app like Button Savior or Shutdown Menu 2.1 (Both power menu apps require root access I believe)

EDIT:
Just realized that you might have issues waking up the device once the screen turns off. Found Wave to Unlock after a few minutes of googling. It uses the proximity sensor to unlock the device. This might do the trick.