The video makes me think of Sleepy's Rig when it was driven by SAB Consulting cross country to Tacoma for a make over. I recall some people in the past had issues with their slides, installing either steel unistrut or 1-1/2x2 angle under the slides to deal with bowing down. This looked like a decent job within a budget and reason to make a sturdy TC again.
I watched most of it. I FF past parts I'm not needing to see. Having a 2000 S&S wood frame TC myself with probable similar issues, it was interesting to me. I have already made some similar repairs to the front but not the rear yet.
Black square at bottom of jack bracket is an awning bracket.
I Made a bottom support using a Simpson framing bracket bolting into the underside of the 2x3 on the bottom of the TC wall. Not perfect but much more stable. It supports from the bottom and holds toward the inside of the TC under the wing beneath the fridge.
I have to do similar work to the right rear where there was a window leak that refused to be fixed until I installed a drip edge over the window. Problem solved.