Installing safety flag with mounting bracket on an Oasis

Just got a new Oasis tandem and want to mount the orange safety flag that I bought with it. Since there's no access to the rear of the hull in order to mount the flag directly through the top of the hull, I ordered the external mounting bracket. I'm wondering where would be the best place around the stern to mount this? There is a nice flat top rail on both sides of the stern, but the cords for the rudder pass through the space under this area and I'm concerned about drilling into this area and damaging one of those. Anybody with experience in mounting one of these?
Thanks!