Teardrops n Tiny Travel Trailers

Not looking for new ideas, wanting to know if someone has an idea of the stuff cargo trailer manufacturers use on the roof to seal seams, vents.
Almost like a pourable material?
Pulling my vent to install a power vent and I like what the manufacturer used (Continental Cargo, Forest River)
Sticks nice but comes up easy with the proper scrapper.

Butyl tape?

No, its a semi fluid material that they seemingly squirt or pour on seams.

You're looking for a self-leveling sealant - available in various formulation such as silicone, urethane, butyl, etc.

It can be applied with small squeeze tubes, caulk guns, or poured from bulk containers. Window manufacturers typically use pressure guns or manual squirt cans.

I've used OSI Gutter Sealant. You should be able to find all products at most hardware or home centers and some auto suppliers.

Dicor self leveling sealant but I'd bed the fan in butyl tape first, then screw it in place, then Dicor over edges, screws, etc.

That's what I did with my Maxxair fan 3 years ago. No leaks.

Hope this helps.