Yes, oiling the underside of vehicles is still a common proceedure. I have my have my Dodge Ram 1500 done once a year. Costs about $100. per application. Although, I'm sure that it would be considerably more for a motor home.
Krown vehicle undercoatingIt is a bit messy afterward as it drips for as much as a few days. Not a problem on grass or a black top driveway, but can stain a concrete driveway. Keep in mind that the coating ("oil") is clear. Not dark as typically thought of when thinking "oil". Seems to work well. I guess I'll find out in a few years.
The Krown Company is Canadian based, but they have many locations in the states that do the applications.