Judging by the 12 year performance of Rhino liner applied in a controlled factory production setting, I wouldn't trust Rhino liner anywhere under the sun or rain... which are the key elements that an RV roof is intended to protect from.
The Rhino liner in my experience was not even inside a truck bed. It was applied to the tops of lift lids on utility boxes, which was not a loading or walking surface. It had nothing to do but just stay put, but it did not.
Within the first year, it began chalking, leaving ugly streaks of it's sluffage staining the sides of the utility beds after every attempt at washing. Within the second year it began alligatoring, with delta like fissures dividing the covering into a craggy cratered surface. By year three, the micro creeks and rivers between those crags began to wash away exposing the steel underneath. By year four, after putting up with more gray drip and wash stains down the sides of the boxes, I was now putting up with rust stains on the tops.
Annual treatments with a variety of savior products has not helped. This summer, after a dozen years of this Rhinoliner nonsense, it is getting powerwashed off and replaced with Line-X, which from my observation, seems a lot more durable when exposed to heat, water, and sun, like an RV roof typically is.