If you want to hide it you can mount it under the battery tray, run the wires through some black shrink tubing and snake it up along the wire harness from the starter solenoid and towards the bulkhead connector.
nah, i'm not worried about hiding it... the car doesn't have a battery tray anyway, it's relocated to the trunk Mine has been mounted to the firewall for years but i'm moving the 6AL to a different car and installing a new programmable unit so i'm debating mounting it somewhere else