This is the stuff we use. It's a liquid with Boric Acid in it. It's like a drug to ants. They can't get enough and it will eventually kill them all (including the queen). We had the misfortune of an Ant Infestation in our trailer one year where they were in the walls and outlets and everywhere.
It took about 2 weeks but we got them all with this stuff placed in the soda bottle caps here and there inside the camper. It goes sort of fast at first with them drinking it up, then they start to slow down. Once we got them gone, I just put this stuff out whenever I see any ant activity around the trailer.