One for Cuthulu:



Quite a few UK trucks have been modified into pick ups up tray backs. Have a look on Difflock.com.

LongArch,
    You might try to contact zukinator-z on this board as he has a sliding glass window in the back of his Tracker.  I can't believe I don't have a good photo of it, only caught it at the bottom of this pic . . .



Here's a shot side of his rig with the rear deck . . .

Thanks Rhinoman.

I was thinking maybee a sheet of KYDEX could be used to form a nice solid durable cover that fits well and looks good then just cut out an opening for the rear window (when one is found).
A small trunk lid could be cut out and I would think it would need a small amount of steel framing to firm it up.

I'll have to look into KYDEX a bit more but it is supposed to be very durable and thermo formable and my hope is to be able to form it to the tracker and trim it for a nice fit.

I first heard about kydex type material from radio control rock crawler guys and they use it to form custom rock gaurds that are durable and help them to slide off the rocks easily.
A 4'x8'x1/4" sheet of KYDEX costs around $313.09 a bit expensive but should be enough to do a complete car (front top and rear cover).