Thanks to Alan (fyrekop) over on mylargescale.com I now have a better idea for building the “Alps” on my layout
Alan is using a method I’d heard of (concrete-soaked burlap over a chickenwire form) but with a twist: he made the frame to hold the chickenwire out of rebar. This means no screwing the form together (just weld), no worrying about the thick wooden frame showing through the shell, and the ability to make almost any shape by just bending the rebar.
I’ve been working on a plan for the mountain (general shape and the technical aspects (tunnel clearance, access hole, etc) and this has me really excited about the possibilities. I’m hoping this new (to me) way of creating a shell mountain will make the project easier and the end result better looking.