I finally got around to making a support reinforcement for the center tunnel. As I began working on the area I realized there are two more cracks beginning to form on the opposite side than I first reported. Here's where all of the cracks are:
I decided to take multiple approaches to remedy this; weld the cracks, weld in a reinforcing rod (1/4" solid round stock) on the inside edge of the large opening, weld in a patch to cover the unneeded open area, and make the reinforcement plate extend well beyond this area where the cracks are. The reason for that last item being longer is due to something I realized about the chassis construction. Most of the tunnel is already double layer thickness. There are reinforcing plates welded on the inside of the tunnel at the rear, middle and front sections, with gaps in between them. Unfortunately there are also extra holes in the sheet metal where those gaps exist, making the areas very weak:
The green arrows are where double layers exist from the factory. The red arrows are where no double layer exists, and where there's holes, making the areas weaker....
In the above pic the leftmost and middle holes (red arrows on left and center) don't seem to crack like the larger front hole (right red arrow) does. But I figured it would be easy to extend my reinforcement plate to at least cover the middle hole (center red arrow) as well as the large front one.
Here is where I welded in the round stock reinforcement inside the top corner:
After this I added a patch over part of that large hole, but forgot to take a pic.
This is the cover plate I made:
And how it fits over the tunnel (need to get more hardware and add a finish paint coat to everything):
The shifter will sandwich the plate toward the front, and the park brake mechanism will sandwich it toward the rear. It extends beyond the double wall sections on each end, making the entire tunnel doubled - except that little hole toward the very rear bulkhead (the leftmost red arrow in the second pic), but I'm not going to worry about that.
I wanted the plate to wrap around from the top of the tunnel and down the sides part way. Additional anchor bolts will go along the lower edges:
The plate is made of the same thickness metal as the factory tunnel, equaling the double layers from the factory. As with the plates made by others, it needs to be removable to access things inside the tunnel.
Then on to redesigning the wire harness/electrical system....that is a huge job.