A few years ago when i was still using my old BMW estate as a tool lugger for my on site kitchen fitting, i built a fibreglass install in the back but i needed to keep it removeable, also the spare wheel was underneath the middle of the boot floor, so i built it in three sections, the centre section housing the sub and amps and two side pods with the 6x9's, all connected with professional bayonet style p.a. jacks and the power source with a bayonet style plug and jack, i built it in such a way that if i needed the spare all i had to do was fold the back seats down and the centre pod would slide forward on top of them allowing me access to the spare wheel and although quite heavy the whole system could be removed/put in, in under 10mins, ill post a couple of pics when i have enough posts to do so.