Lots of stitch welding and seam welding followed, while awaiting delivery of critical components (namely, suspension). There are loads of resources and articles online pertaining to the critical areas to weld on an S30, so let those be your guide. Obviously, it's not hard to get carried away.
With the stitching reasonably complete, and some known-redundant holes filled in, it was time to fill in that gaping hole in the deck where the spare tire well used to be - that's where we're going to put our new fuel tank.
With the car flipped on its back, the underbody becomes an easily-accessible work surface. I started by making a cardboard mockup of the tank I intended to use, so that I could design the filler neck, straps, bracing, and access hatches. As it turned out, a UT-N-2HT model (Universal Pickup Truck Fuel Tank with Fuel Injection Tray from Tanks, Inc) was the perfect size for this application, and it's already nicely baffled and set up for fuel injection.
Extra bracing and relocated straps will center the tank neatly under the deck, and the access panels will allow servicing the pump and sending unit in the future. BTW, the access panels are steel electrical box access panels from Home Depot. They're strong, square, and perfect for this purpose.
During this process, I thought long and hard about how to handle the fuel filler situation. Keeping it stock-appearing would mean somehow incorporating the fuel door into the extended fiberglass fenders, which would mean a lot of engineering just to retain the fuel door. Filling the tank via a cap inside the hatch is tacky, unsafe, and not appropriate for this level of build.
"Boy, remember the good old days, when the fuel filler was hidden behind the license plate?"
Damn right I do. And that's perfect. A musclecar-style filler port behind the license plate would be perfect. In fact, let's get really trick and use a spring-loaded plate frame AND a modern push-through fuel cap (so no need to remove the cap).
More to come - Gotta get back in the shop and make some more sparks!