Sooo.... today I learnt quite a bit about the car tbh after having to take half the interior trim out! I went to a friends garage and had some help fitting my sub and wiring my head unit to an ignition live.
So the first task was to wire the power cable through the bulkhead.. which turned out to be a mission but was achieved in the end! We had to remove the wiper blades, to try and get the rain tray out, but it was held on too well and we couldn't find any clips or anything holding it on. So in the end we just pulled it out the way and were able to find a grommet that came out at the top of the dash, which meant removing the glove box. Then we ran the cable down through the car under all of the side trim, up into the boot where the sub sits. Then found an convenient hole to poke the cable through to the battery from under the scuttle panel, which meant removing it again! Once that was all back through again, we ran the remote line down as well.
Then we removed the other side, and wired the RCA cables down there. While we were at it we ran a cable from the head unit to the fuse box so that I could avoid spending £50 on a CAN-bus adapter just so it comes on and off with the ignition!
Then we had to remove all of the boot trim, which took a while to figure out how it came out due to there being no screw holes etc.. It wasn't too bad in the end, and a little bit of pulling force unclipped it. Overall it wasn't too hard, and I now have my sub installed with no cables showing what so ever! Not even in the engine bay which I am pretty happy with!
Only took one picture, and it came out badly to say the least!

Also had a tinker about with a 200sx fitting a new gasket on the manifold and turbo

Next up (tomorrow hopefully) - I'm going to attempt to re-wire the rear speakers directly to the head unit so they aren't running off the (somewhat underpowered) Audi amp thats in the boot! This will hopefully make them equally as loud as the front speakers (currently on -8 fading to the rear!!) and stop the horrible crackling noise thats coming from them at the moment (common problem when using a wiring loom that doesn't use RCA cables to connect the Audi amp to the head unit).
Going to need a lot of luck I think as I'm on my own tomorrow!