Rust-Oleum Leak Seal vs Flex Seal

I question whether either product is suitable for RV which flexes etc. If it were me I would have the rig pressure tested - find exactly where the source of the leak is and use whatever product is suitable for the identified leak. In my case I ended up using Eternabond tape on side seams as well as front/rear seams.

I'm still dealing with the cabover leaking on Minnie Winnie...am considering spraying all side seams, windows, etc.

Rust-Oleum is the better quality product, but you don't want to spray it on a rubber roof if that is where you problem is. They both contain solvents that could harm the rubber membrane.