With a bit more experience (in masking) and thought about how the prime plan is to work I moved back to the vertical stabilizer assembly to mask the spar and end caps.
As the intension is to have all parts making contact primed in the contact zone, and the remainder is left undisturbed alclad some thinking has to go into what to be left to be primed and what to cover not to prime. The inside of the rib does not need to be primed unless another surface is connected to it, for instance.
Minimizing the prime areas also reduce weight - at the end. This is a heavy prime to be used.
