I wonder if it is really a 20-watt per channel amplifier. Of course, it doesn't mention the speaker load it will deliver 20-watts into, but it does say it is 20-watts per channel RMS and it operates off of 12-volts DC. Unless it has a DC-to-DC converter to step-up the voltage, it seems like it would ...
Upgrade to AMP-1003E Elite Series lockers which include a 3" wide 18 gauge full height door stiffener spot welded to the inner door face and MIG welded to the hinge side as well as to the top and bottom door flanges providing a rigid torque-free door. A 1-1/2" wide stiffener will be furnished for 9" wide AMP-1003E Elite Series lockers.