Every couple of years, this topic bubbles back to the surface and it always surprises me just how much emotion seems to come with it, especially from those who have not actually used it themselves. Why this should be, I can't begin to guess.
So, again, here is my own firsthand experience -- with PROs and CONs, and before-and-after pictures:
PROs
1. EASY - I had two strikes against me when I started this project: First, as a youngster, I was lazy and disliked anything resembling hard work. Second, the passage of seven decades has now made me a cantankerous old geezer, who hates manual labor even more. While this job is lengthy, it is not strenuous; nor does it demand speed, you can proceed at a leisurely pace. The most arduous task is the initial wash, and that depends on the initial state of the coach's gelcoat. No buffing, no rubbing. Just wipe on a thin, watery coating.
2. CHEAP - Another of my failings: I am a cheapskate. A $20 gallon of ZEP will do my 38-footer, with almost half remaining.
CONs
1. NOT PERMANENT - In constant sunlight, it looked great for about two full years, but the gloss virtually disappeared over the next six months.
2. NOT PEFECT - a really close inspection will reveal slight surface waviness in the gloss, unlike the mirror-smooth finish of hand-rubbed wax/polish.
RESULTs - it looks wonderful!
Many people who have told me that my 20-year old coach looks like brand new. Not a single one has ever added, "...except it doesn't look as good as a hand-rubbed job."
I just re-coated my coach after 3.5 years, but this time the preparation was a simple washing. I did not notice any yellowing, and I did not strip the old wax. In areas that were not hit by the sun, a single coat restored the shine.
Here is my original post with all the info (and pictures) about the ZEP process (previously called "Red Max Pro").