I'm not sure about the 192 shower. In our 2016 179, it has wallpaper. It has proven to be effective. We use a squeegee followed by a microfiber cloth wipe down after showers to speed drying of the walls. Since we bought it in December, 2015, we (my wife more than I) have  used the shower many times.

I would not worry about it. The plastic surround has its own problems, such as not sticking to the wall behind it from comments I have read in other topics. I agree with Fred in this respect. Observe and address if needed, but I trust Forest River on this.

Paint may not stick well to the surface and would do little to stop a leak.  If you are really handy, you can buy material from building supply places that can be applied over the existing walls.  

Personally, I'd let sleeping dogs lie unless you have signs of leakage.  Probably, the walls, as constructed, are sufficiently waterproof.  All you need to do is clean them with a mild household cleaner and a soft cloth or paper towel.

We dobbled up the shower curtain in our 172 and cover all the bathroom walls with the curtain.