just use your hands.
i just brign aroujd a water bottle or a liter soda bottle depending on how many posters, and then 1 latex glover per poster

then u just pour some onto the wall from the bottle, smear aroudn to appropriate size with ur hand thats gloved, put up the poster with ungloved hand, thne pour more on top and smear out all bubbles with gloved hand, thne toss teh glove