Pro tip: search through google via "site:skoolie.net ceiling" or replace ceiling with whatever you want. Check out the image search section too, it helps me lots!
Are you doing anything to treat your sheets beforehand? I'm doing something similar for my shower install with 1/4" underlayment from home depot. I got mine in using a very ghetto setup. I left it overnight over a sawhorse with weights on both sides. I wet both sides a few times with cold water (warm is supposed to be better).
Then I pushed it up against the ceiling (there were some cracks, I'm still not 100% sure if I'm going to try and redo it.
but it looks good for now.
If I choose to do it again, I'm going to buy a cheap garmant steamer from Wally's and steam the crap out of it while gently applying pressure. I would imagine it would work better, but everything works better in my mind than reality.
Jazty did a great job on his Armageddon bus build.
by scoring the wood. I tried doing this and failed.
Could also be good to take advantage of return policy and consider using FRP or polywall.
I used polywall, it was a little too flexible, but I like how it turned out in the end. #feelsgoodman.
Best of luck to ya mate.