Does anyone know the purpose of the small plastic tank held into the inside of the convertible fuel tank (1989)? Looks to be about one gallon and held in place with straps.

I'm guessing it has to do with the evap. system but cannot see anything connected to it.

 

Its purpose is to catch any dirt, debris, or water that may be present in the tank. This way, these contaminants can be removed before they have a chance to enter the engine.