For those of you who want more bass but don't want to sacrifice your spare tire or hatch space, I highly recommend this spare tire mount subwoofer : r/GolfGTI
Awave AST-11TV4 11" active spare wheel subwoofer – SoundQuality.net
Cerwin Vega ACTIVE and PASSIVE Spare Tire Application Subwoofers Series | eBay
Spare Wheel Active Subwoofer - Emphaser
Subwoofer Box as a Spare? Volume Calculations + Build - CarAudioFabrication - YouTube