Both A's and C's can benefit from a Rear Track Bar. Also known as Panhard Rod (or Bar) it's common in cars, even minivans/SUV's. Not common as OEM equipment on trucks. Maybe box trucks don't need it as badly as RV's. RV's have stretched wheelbases and rear chassis overhang extensions.
Class A's with one-piece FRONT axles can benefit from a Front Track BAR. C's, like some A's, have Independent Front Suspension/IFS. IFS has Axles or A-Frames, Wishbones, etc. attached to the Chassis, so a Track Bar link to the Chassis isn't needed.
Neglected to mention earlier: JAYCO, to their credit, has addressed some of the OEM chassis deficiencies with their J-Ride enhancement. It's a Hellwig rear sway bar and Hellwig helper springs, along with rubber frame-to-chassis insulators. Our older Jayco has those isolators, thought they all did, but came with nothing else.
I've mentioned Henderson's in Grants Pass OR. They didn't invent the Track Bar, but they discovered the need for one on RV's when they noticed rubbed spots on the sides of the rear leaf springs on a Class A. They offer rear track bars in their Super-Steer line, but not front. Eric Davis (Eric's RV) in Sequim WA process the Davis Tru-Trak bar, only for the fronts of Class A's.