We have a 2013 Cougar 323MKS and it has an EDPM roof. We use Dicor self-leveling sealant.
https://www.amazon.com/Dicor-Self-Le...s%2C112&sr=8-2
Here is a video from Ray. A full-timer in a Cougar that has helped me with tons of questions when we got our cougar. Check out all his reviews. they are just what I needed when I had questions about almost everything in a Cougar.