Just bumping this up
I bought some seat covers almost a decade ago I guess. The came from a big box auto parts type of store. I've used them in 4 RV's now - I just reuse them, moving them from one RV to the next. I don't remember the brand but they're probably not still made anyway. They were not expensive.
The tightest fit was on the Roadtrek I had. It was a height issue not width. The RT seat back was just a bit taller than the seat cover. It worked good enough though.
I had to cut a slit and hole for armrests. Some armrest pop off easily and some I can't figure out how to get them off.