Since my hull sheer line strip and deck sheer line strip are currently touching (not glued together but in apposition) on the forms, there is no way to insert masking tape between them

If the plan was to remove that '3-strip assembly' later, couldn't you just release it to allow putting tape where you don't want the strips to bond with epoxy?

It's a hassle, but not a disaster, if you need to use a thin saw blade to cut between strips that have accidentally been glued with epoxy. (How do I know? ;-) )

BTW, clear packing tape is something to add to your toolbox for work like this - epoxy will not stick to it, so you can cover wood (or better, masking tape) with the clear tape to prevent bonding. Packing tape can leave a gummy residue behind, so I often use masking tape on wood then clear tape over that.