I've gotten the canvas fitting muslin almost done now, except for some more markings and basting eyelets on the back (and figuring how I want to do makeshift boning casing for it). Here is a pic I took earlier today, before I became exasperated enough at the fraying to overcast the outside edges:
On the pattern tissue, the waistline is marked on the CF and CB panels, and the line goes around the waist very neatly. I also need to mark the CF line on the fitting muslin, although I plan to use a zipper and will need to leave a space for that.
As for boning casings for fitting muslins, I am thinking to construct some canvas tubes with finished flaps to either side that I can hopefully baste on then remove.
I've done mostly thinking on this today, as I woke up with a headache and an achy back and neither seems too inclined to leave just yet.