i also have another idea i may try. I'm not ready to rip just yet.
I kept piece of door stripping, brand new, never used. it's got to be 6-7 feet long and I have a 48 architects ruler too, and squares etc. men's tools are cheaper than ours.
anyway, i don't see why this metal stripping wouldn't be like a super long straight edged ruler. gonna see how i do with freezer ppr first. That is, if my current way did not work. I think it did. (the usual folding)