Filter Filters GMC Remove All Filters Price $100-$500 (57) $500 and above (1) Condition New (58) Brand Harmony Audio (58) Model Sierra (54) Canyon (2) Envoy (1) Sonoma (1) Compatible with 1999-2006 GMC Sierra Ext Cab Truck Harmony A122 Single 12"... $396.99 1999-2006 GMC Sierra Ext Cab Truck Harmony R104 Single 10" Sub Box Enclosure $145.99 2007-2013 GMC Sierra Extended Cab Truck Harmony R104 Single 10 Sub Box Enclosure $136.99 1999-2006 GMC Sierra Ext Cab Truck Harmony R124 Dual 12" Sub Box Enclosure New $247.99 2001-2006 GMC Sierra HD Crew Truck Harmony A122 Dual 12" Sub Box Enclosure New $255.99 1999-2006 GMC Sierra Ext Cab Truck Harmony A122 Dual 12" Sub Box Enclosure New $275.99 2007-2013 GMC Sierra Crew Cab Truck Harmony A122 Dual 12" Sub Box Enclosure New $290.99 2007-2013 GMC Sierra Ext Cab Truck Harmony A122 Dual 12" Sub Box Enclosure New $245.99 1988-1998 GMC Sierra Ext Cab Truck Harmony A122 Dual 12" Sub Box Enclosure New $280.99 01-06 GMC Sierra Non-HD Crew Cab Truck Harmony A122 Dual 12" Sub Box Enclosure $255.99 1982-2004 GMC Sonoma Extended Cab Truck Harmony A122 Dual 12" Sub Box Enclosure $260.99 123