I have three 12v actuated gun drawers for vehicles. They were made to mount in the trunk of a police cruiser to allow secure access to a carbine. They are made by Estes AWS.  Dimensions are 39x17x8. Would be perfect for under the rear seat of a full size truck. You supply 12v through a hidden switch, a solenoid pops the drawer and a gas strut opens the drawer allowing access to your goodies.  James Bond type stuff.  I have one key. 

they must be top or side mounted

located in Stoneville nc. 
704-277-99forsix