Once I decided to go the fuel cell route in my 240z, one of my biggest concerns was what to do about all of the huge holes that would be left behind in the hatch area, not only simply for comfort (noise and air quality), but also to pass tech for autox/track events. I enlisted the assistance of a fantastic fabricator buddy of mine (thanks Max!), and this is the (mostly) end result:
For those just interested in pictures, the full album is here:
What we decided to do was cut a hole parallel to the hatch floor. What this did was leave behind a nice perfect (70's-ish) circle, and wider recessed circular area where the cardboard cover sits. Then the idea was to fashion a cover to essentially sit where the original cardboard sat, but fastened through the sheet metal in the hatch.
Of course, the next issue was figuring out how to create an access area for servicing the cell (feed, return, etc.), and more importantly refueling! After searching high and low for over-sized fuel doors for trucks and other assorted applications, one day I was just staring into the hatch space trying to brain storm and I noticed the factory tool doors. Perfect! Not only is the opening big enough to fit your entire hand in, but they're wide enough to cover virtually all of the serviceable components of the cell! I was able to find a used Z tool door quite easily off of eBay.
We then sourced a large enough piece of 18 gauge stock sheet metal to cut out a 27.5" diameter hole, and sent the stock and tool door off to a local waterjetting shop. They were able to cut it to 27.5" diameter, and also cut a hole slightly under-sized for the inspection door:
From here, I ordered 25 feet (15 would've been plenty, but I make mistakes and wanted extra) of X-1015 U-channel, for both the outer edge of the cover and the inner edge of the inspection hole:
We then drilled 8 holes for fasteners, 1/4" in from the outer edge (to sit dead center on the U-channel), and 22.5 degrees offset from center (of the front of the car, offset because of the chassis supports behind the diff and in front of the tail lights). We also drilled 4 holes for the inspection cover:
As a happy coincidence, the new "3rd Z tool door" happens to sit almost dead centered with the factory ones, as the cell sits as far to the passenger side and as far forward (weight distribution) as possible:
It could use another paint-job to try to clean up some of the flashing, but all in all I'm extremely happy with it. It should be both air and water tight, and provides as-good sound dampening as the original spare tire well.
There's also the matter of all the original fuel hose holes (I can't believe it was even legal to run them into the hatch area, considering it isn't isolated from the driver's cabin). I used this kit, which worked to plug up ALL of them, except for the original fill hole:
Picture for reference as the auction will inevitably end:
For the original fuel fill hole, we'll just be making a small square cover, and using the original 3 bolt holes to fasten it down... and that should be that!
Please feel free to ask or PM me any questions, happy to help any Z owners to sort through this daunting task!