I would use this, might work for you.
https://www.amazon.com/Heavy-Duty-E...rd_wg=CMKpb&psc=1&refRID=388KW5C7WES8E5ZEJQ82
If you don’t want to use card board I’ve had good luck making patterns with clear acetate. Just tape the sheet into place, trace your desired outline with a sharpie, cut with scissors, and transfer the outline to your finished material.
This has the advantage of allowing you to see through the pattern material to trace the desired shape.
or use the gravestone rubbing process with a wax crayon. I will use mat board rather than cardboard. poster board is too flimsy. start with the easiest panel and work your way down the drain.
depending how you will attach them, there may be a need for hand access. on the GMC, I used these: https://www.amazon.com/Parrishs-Mag...srs=2598199011&ie=UTF8&qid=1521794442&sr=8-10 cut into the door panels with the intention of framing them and adding a couple of cross bars to hold soft goods. there are a bunch of different sizes. haven't quite finished that, yet.
if you ever need to access the door cavity, or hide contraband, it's a simple matter of unscrewing the box rather than take the whole panel off.
This idea, but with a thick clear poly tarp. Temp-tape it on the interior like a drum head skin. Then you can also mark any support bracing for drilling holes for attachment hardware. The OP is talking about interior skins, correct?
Are these aluminum? I looked through the description and didn't see it. Do you know of any in stainless?