Be sure to have a sharp pin handy to ever-so-delicately pierce the print to let out trapped air. Those trapped air bubbles look even uglier than a pin prick. OK, who snickered?
This takes practice. Don't use a hard tube. Instead, arrange the print into a big U-shaped curve (not touching the foamcore) taped down at one end. Grasp the loose end of the print with one hand. With a cotton-gloved other hand, as you move the U of the print ever so slowly forward, push down on the print at the center, working the push out towards each edge. 1 inch at a time. The top of the U will above the gloved hand. Maintain the U curve bend as close to the point of print/adhesive contact as possible, that rigidifies the print as it goes down in a way that removes trivial, bubble-making ripple. Gets harder towards the end. Worked well for me using adhesive mount. Except by a few years down the road most of those prints had developed really ugly air bubbles under glass. Have a nice day.