, the color is in the material, which is a topical layer on the outside of the fiberglass. (It's actually applied in the mold.) With prolonged exposure to sun, it oxidizes, leaving a dull, chalky finish. As you correctly say, a good wax will retard the oxidation, but not completely stop it.
You're also correct about the effort required for badly oxidized gelcoat. However, I warned about not going too hard with the abrasive because it's possible to go right through, leaving no gelcoat. This would not normally happen with hand buffing, but certainly could if someone used a power buffer.
When we do the boat, my preference is to do all the oxide removal and subsequent application of carnuba paste wax by hand. It consistently takes 21 days. A motorhome has much less surface area, and typically has less direct sun (except the roof). If done regularly, upkeep of a gelcoat motorhome exterior is not a huge amount of work, and can be achieved using the 3M liquid product, but it's not a free ride.