Looking for advice as to how to protect this little gem from the elements. I've seen advice here on just about every subject imaginable so figured it couldn't hurt to ask!

For Christmas, my wife and I got my parents a brass mailbox from Restoration Hardware, and my wife painted a portrait of their dog on it using acrylic paint.

This is a bit of an experiment, as she'd never painted on metal, and never for anything that will be outside exposed to the elements.

In the first picture, you can see how rain has caused a bit of streaking/running paint from under each paw. (I messed with the brightness/contrast of that pic to hopefully make it more visible here).

She has some Krylon Kamar Varnish (#1312), but it looks like that's more to prevent yellowing than provide weather protection. I checked the Krylon website and don't see any weather proof clear coats.

Any suggestions for a specific product that could weather proof this painting?

Linky to mailbox info