The first setup they welded across the ends of the subframe. That's not a great idea. You should never weld across a frame flange.
If you look at how the factory adds tubing to the bottom of an ibeam, it's stitch welded down each side. That lets it flex without creating a stress point.
The second why looks better buy an xbrace between them and stitch welds the sides would certainly help.
I added some tubing to an rv years ago, 1.5 inch square. Stitch welded the sides and reattached the hangers. tow another 7 years or so and it was fine.
But we all know rv frames never crack or have trouble anyway right?