Well, fuel usage depends on whether my wife is in the car while I'm out cruising...
We've taken two hour rides without having to stop. But then again I've burned thru 5 gallons in twenty minutes. I wish I had a digital cam. I would have posted some pics already for you. I'm in the dark ages in the electronic gagets area. I have to bring pics to my sisters house so she can scan & e-mail them back. If your Shell Valley trunk hasn't changed from my 1990 design the cell should sit approx 1/2" lower than the rear axle 'hump' The cell I used is 26"w x18"x 9"deep with a 2" sump with rollover protection and there's a 7" space between the cell and the trunk latch mech. area. 15" area to the left 18" on the right which is where I mounted the battery box. I don't know what others need to carry in their Cobras trunk but my 2 folding chairs and duffelbag of sweatshirts/jackets and sack of emergency flares, emergency tools & emergency cleaners are all I need. Whew! like they say 'a picture's worth a thousand words' I think I may have hit 1000...Hope this helps ya.
Ed