The bottom plate will complete the structure on this side and is ready to be welded in. I ground the edges again, taking away an Kitty-hair that got close to the welding area. The inner part of the plate was sprayed with several coats of Rust-Bullet, a new to the market, single part, moisture-cured resin in the same category as POR15, but with the added benefit of having full UV protection.
I held the plate to the torque box with several items, including this bottle jack and a couple of sections of pipe. Beginning with several tack welds, I then turned up the voltage slightly and ran 1" long beads, alternating from side to side, until it was welded in solid.
I dressed the initial welds then went back and filled in any gaps. The plate was solid and the box was now complete, except for some finishing work.
After a thorough cleaning with Pre-paint solvent, I coated the welded areas with a thin coat of kitty-hair. This stuff dries so hard that - if needed - would add another layer of structural integrity. It certainly wasn't required here, as this 12gauge plate is the heaviest material I've ever done repairs with - but it is important, mostly to seal up the repair and secondarily to smooth it all out.