roachie

It looks like the sub box is the go, now my only issue is the trim in its place. I can get the 4 bolts out easily enough, it's the 2 rubber hoses that are giving me grief how do I get around them? And how has everyone mounted the battery in that area??

Yeah, the switch fits in the one of the blanks perfectly too

That could work, my main concern would be the lack of cranking power it would have though

Looking at moving the battery to the rear but every guide I can find requires the removal of the spare wheel, does anyone have tips on how it could be installed without removing anything like that? I've been trying to find a way to mount it at the rear left as there's plenty of room but the surface is uneven.

There's a much easier way without using the ECU or stock switch, if you get some twin-core wire and connect it to the top two spades on the spoiler itself (the big ones) you can run it through the engine bay into the interior through the grommets. From there you can get power from a fuse or the back of the 12 volt plug and connect the wire to the middle spades of a double pole double throw switch with diagonally opposite spades joined. Doing this will allow the motor to run both directions depending on which way you've pressed the switch, as it doesn't use the ECU there's no limitation on when you can put it down or up.