So thats the final result in my idiot saga. Doing it the right way, it seems almost fool proof.
I had some bubbles cause of shit getting in there, but i peeled it up and put it back down a few times and its pretty damn good. The corners are fucked cause the adhesive there is gone to shit. But everywhere else... pretty flawless (other than it being covered in shit on the inside cause I had it exposed before. Doesn't bubble at all really, you can just see the shit locked behind there.
So let that be a lesson to you gaf, pay attention and it should be super good. This whole process started me hating the fine folks at amfilm, but for as much fuckery as I bumbled into, it still went on great despite it. So 10/10 amfilm.
The shower room is probably bullshit, its not needed. The hinge method is good enough and making sure its clean.