how to unwrap this simple window frame? I'm fairly new to 3d modelling and I've been working on my UV unwrapping lately, I've had problems with this object for a few days and was wondering if one of the pros / semi pros can help me out...
The object is a simple window frame.

The issue is with the inside part of the frame has warped UVs as you can tell from the photo below. Where else do I need to mark a seam to fix this?
The issue with your unwrap isn't the seam placement, it's that you didn't uncheck Fill Holes in the unwrap dialog.
This is probably way overkill, but here is the layout I came up with that uses the least amount of visible seams as possible:
Top:

Bottom:

The layout: