Heres all the boot builds I have done, well, I say boot builds - just speakers in the boot.
First installBut I used to carry passengers all the time, so the weight wasn't practical. Although it was only 6" deep, had 1x12" sub and 1x8" sub and two 5" mids. It was covered in OEM carpet and looked pretty ordinary (which is what I wanted). Made out of 12mm MDF. Sold on eBay.
Second installIt was a 12" sub with a basic 100w amp. Sold to a mate.
Third installTwo 12" subs in a 2 chamber sealed MDF box (homemade again) covered in Vinyl leather.
It kinda uses more bootspace, but has better volume for each sub (2.5cuF) and is completely air tight and very sturdy. Plus I tuned it to the frequency I wanted. It doesn't fit in the boot of the Golf, plus having 2 subs is silly - only used them because I got them cheap.
Fourth install Wheel arch build so I could still have bootspace and get to the spare wheel.