It's 1/8 inch plain steel plate, 4 inches wide by um... 18 inches or two feet long, from the Home Depot. I cut it to 6 inches long with a fiber chop saw from Harbor Freight and drilled the holes on a drill press. This plate actually bent slightly around the torsion bar under the force of the bolts, and I think the support bar is also bent the same way, but it's no problem. It's soft steel, easy to work.
The final should be a lot neater. I didn't set this one up carefully with bluing, a scribe, and a punch, and I didn't file or sand anything. I just drew marks and aimed a large drill at them.
I'll probably leave the catch alone until it acts up, as I've a lot of other work to do to accessorize the trailer. But it's good to know someone's already worked out a way to reinforce that part, and thanks for publishing your work on it.
I'll look into Lowes. There isn't one as close as the Home Depot, but I pass two on the way to a customer in San Jose.
By the way, I'm not making money from
perens.com/rv either, but hey readers, if your tech business has compliance or intellectual property issues, see
LegalEngineering.com :-)