dicor self leveling lap sealant on slide out roof?

How can water get trapped under it?

I believe the only reason they don't use it "more" in RV manufacturing is because of the time and expense to apply it. Go ahead and look up a couple youtube videos of the typical manufacturing process and you'll see a couple guys racing through the construction process, almost literally running along beside the new unit as they lay down the caulk or lap sealant.

There are manufacturers that do use it.