For me I always draw my designs on the shell with a Sharpie so I just have to look on the topside of the shell and I can figure it out from there. If it's really hard to find I use a bright light behind the shell so from the inside I can see exactly where my lines are.
I don't do very intricate stuff atm so it's not a massive concern
. You're shells are cool Max I'm sure you'll find a way that works.
J