Last resort Christopher.....Cut the rear cab glass rubber.
It might be cheaper than calling a locksmith!
P.S. Why did you install the rear with the lock strip inside?
Was it for looks?

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.