Aye cheers, might hit you up about it later on. I only ended up stripping back the 5cm for where the beam plate welded in, there's none after the front beam, it dips straight into the rear seat area. All of that sound deadening has long since deteriorated but I don't think it's the same type stuff as in that boot area.
Late nights, paint fumes and bonus missions.
Rear beam top plate welded in and my mate worked some magic to butcher the old cover plate and weld it in well enough that it doesn't look too much of a disaster. Had to trim the boot plastic trays to fit around the new beam, and the old panel had to be carefully aligned so that the two studs fit correctly with the holes in the plastic bits. Don't have those issues on coupes... Small frustrating thing is that the central trunk cover won't align properly now. Had the top beam have been just 5mm shorter it would have fit perfectly, but as it stands, the inside face of the cover hits the back of the beam and won't sit properly over the studs. Will see if I can trim the holes a bit bigger and make it work or will have to cut off those flanges altogether and screw the front of it into the plastic somehow.
Primed, seam sealed, primed again and painted with some gloss black I had from fixing up a small rust patch on the rear door sill. Looking back, should have just kept it primer grey as the gloss black sticks out like dog's balls back there. Luckily, it won't be too visible and the main thing is that it's protected.
Onto the underside, test-fitted the subframe to check alignment, all looked fairly good. Ground down any remaining high spots, primed, seam sealed and enamel coated. The colour match turned out to be miles off but will be mostly covered and should provide good enough protection from the elements.
Pretty satisfied with how the wheel arches came out. Managed to lay on the seam sealer thick enough to almost match the surrounding rubbery underseal texture. After some primer and enamel top coat, the whole thing looked horridly out of place and with this area being more visually exposed, I popped over to Supercheap for a couple of cans of black underseal and gave it a few coats. It went on well to the rest of the arch but wouldn't stick to the enamel properly, even after some rough scuffing effort. Took a few times of going over it to get a decent finish but ended up with tidy black arches that I'm quite pleased about. Forgot to take a photo of it though.