Teardrops n Tiny Travel Trailers

I've seen this referred to in several places but have not been able to find a post that explains it. I think is must be some sort of liquid covering for canvas, but that is the best I have found.
Thanks for answering my silly question. It is probably common knowledge to most of you.

Tight bond 2 glue

To correct the spelling, Titebond II

Only purchased by the gallon, not the oz