I've used ProtectAll for decades, and it does work. But I've noted it can break down in its container over long periods of time, so purchasing it in the gallon jugs wasn't as cost-effective as I'd expected.
Although it's pretty spendy, I've more recently been using AeroSpace 303 instead, and I think it has more UV protection than most other products of the same ilk. Regularly applying it to the front cap (once a week to once a month) while on long trips does make cleaning bugs and dirt off a whole lot easier. I haven't tried it on the roof, though I did once use ProtectAll topside, with results like Bill's. But Monaco's recommendation of Maquire's was used a couple of times, and though much harder to apply, I think it lasted longer before the oxidation started reappearing.
My brother has been into restoring old cars for most of his 77 years and knows protective techniques - he subscribes to just about every restoration periodical, and via the articles he keeps up on modern paint, technique, and protecion technology. His advice to me was you just can't avoid hard work. No matter the product, UV protective chemicals only last a few weeks when exposed to the sun. He did his level best when we first bought the Monterey to talk me into a steel carport for it, but after the coach purchase there just was no money left. He spent several hours one day driving me around East Portland showing me houses with big RV carports. He was so insistent I half expected him to offer to pay for it himself. He's always wanted a coach so bad himself, he can hardly stand it; his wife will have nothing to do with riding in such beasts, the poor guy. But even if cost had not been an issue, the logistics of such an installation in our already confined RV pad area just wasn't feasible.
So I try to polish Mequiar's onto the roof when I do the coach overall; even if the UV protection expires soon after, it still seems to mitigate the white oxidation that washes off, apparently for well over a year. 303 in a quart bottle should spray and spread on up there easily, so I want to try it next time. A downside to wax, ProtectAll, or Aero 303 is they make the roof slick, at least for awhile. So I try to get anything else done up there first, like AC unit checking, seam checks, vent lid seal treatment, etc. And I try not to finish the roof just before tripping off to Bend and having the guys do any work up there - they'd not expect a roof to be as slippery as that.
Ultimately we should probably all be applying Ed's paint technique. I've just not found the time to do it or I would have by now.
Joel