I tried all kinds of things on my old RV. When I bought it the previous owner had scrubbed it down and used the EPDM products off the shelf from CW. It didn't last at all and came off in sheets. I then bought a 5 gallon bucket of EPDM liquid rubber. That was nasty to work with but actually worked pretty well, for a while. It dried real slow and with the 5 gallons I was able to refrigerate a gallon and several months later go back over a few spots and touch it up. In a few years that started failing. I used another gallon or two and really struggled to get the leaking stopped.
(Not recommending this) I asked around and a buddy had a small leak while on a road trip and fixed it with something from Lowes, Ultra 1000 something or other from the roofing section, it comes in white. It's a roofing repair goo, not EPDM at all. I cut out the wet stuff and let the open wounds sit in the sun for a day. I bought 5 gallons and as a last ditch effort to save that old roof rolled it on. It sealed and the RV stayed dry all year. The downside was that I had to get back up there with a gallon every year and recover a few spots that looked like they were needing some attention. Yea, it's a redneck fix for sure. It worked and never had another leak after that. The can says it can be used on RVs but, I guess they are being very liberal in their interpretation. The downside is that if you use it you're probably permanently going to be using that product as nothing will stick to it except more of the same stuff. Nothing, not even Eternabond will stick to it. If I had an old beater RV that I needed to fix the roof on and didn't want to invest a whole lot of time and money I'd use it again. BUT, I DO NOT recommend that you use it. It will ruin your roof. Yes, it will keep things dry but, your EPDM days will be over. It's a long term relationship. Also, don't do anything to trap water under the rubber. It will never dry, not in our lifetime.
The best solution is buy a big roll of rubber and recover the roof. Liquid products are a temporary fix.. Of course, no fix on a rubber roof is ever truly permanent. The best thing is to find problems early, real early. A real close inspection twice a year is minimum.
