08-11 FORD FOCUS SUBWOOFER & AMPLIFIER BOX ASSEMBLY 9S4T-18C804-BA OEM | eBay
Audio Upgrade in RHD RS (NOT the US version i.e. no factory sub/amp/FENG) | Ford Focus RS Forum
2012-2014 Ford Focus Sony Subwoofer Speaker Rear Trunk sub woofer black H335 | eBay
Columbus Car Audio on Twitter: "Custom built subwoofer enclosure and amp mounting in the cargo/trunk space of this 2016 Ford Focus RS. So yes, you can have awesome sound without giving up