rotate and mask

[mercphoto]

I'm looking for a technique in Photoshop to rotate a rectangular image by 10 degrees counter-clockwise, then put a reveal mask on the rotated rectangle. I can do the rotation part. The problem is when you copy that layer to another document I want only the rotated rectangle to be visible in the new document. And I don't want to have to make this mask manually. It must be an exact mask.

Does that make sense?

[mercphoto]

Sometimes I am soooo stupid. The obvious answer is to mask BEFORE you rotate. Rotation will then rotate your mask along with your image. D'uh.

Duplicate the background. Select all. Add layer mask as a reveal selection. Extend the canvas size in all four directions. Rotate canvas. Voila.