Just want to verify that it's okay to seal a moving gate on the street?

Esto said:

Nope, gates can only be sealed on unstable locations. Sorry. It's in the Lurker rulebook, under "Closing and Sealing Gates".

True, and I've taken this to be a universal rule, as well. That means that if a gate is opened in a street by an Exhibit Encounter, or if someone uses the Naacal Key to open a gate in a stable location, neither can be sealed even if the Lurker expansion isn't in the game.