OK,
I have never shot true bunker, the closest we have around here is what we call wobble trap, some call it international, where it's shot from a regular trap house with a wobble trap in it. The more fun (challenging) places to shoot it also put it in the 3 or 4 hole, (not sure which, but know it's wider than the 2 hole) and speed up the targets too.
Having said that International clays would be a good powder for what you are looking to do. They have loads listed in their loading recipe manual.
I use either clays or red dot for the 1250 loads that I make along with a downrange XXL pink wad, which is a direct substitute for the winchester WAAL gray wad. I really like the XXL pink wad for th 7/8 oz loads in remington and winchester hulls.