If you add the rear window you can remove the side mirror. on my car that was worth 1.6 MPG. Even with a window you can still lay down back there. I have done it in mine. You might want to add a wooden frame and mount a cheep set of blinds or a curtain
It looks like you will need to redo the angle of the top anyway so that would be a good time to do it.
Do you ever get over to Michigan? I would be interested in comparing our tails
Is there anything you want more pictures of or user data on my car?