rust delamination on exhaust manifolds

Is there a way to prevent or stop rust in the manifold exhaust runners (connection between heads and exhaust manifold)?. When I did the engine I clean all the rust out, with a wire brush etc...then painted them back with high heat paint. The paint in the held ok in the upper parts (triangle and risers), but peeled off in the runner a couple of minutes after it got starter...
rust has return again and you can see some delamination around the SS allen head bolts (culprit?). There´s still plenty of material left in there. but i´d like to somehow stop the rust...no water leaks.
I will try some pictures of the actual condition next time i get to the boat.