Most of the larger maps that I've seen are laminated on both sides. Adhesion to the laminate is difficult, the cold roller mount for external use would be my favored choice.The issue with mounting laminated pieces is the unknown amount of moisture in the paper. The heat from a press of any kind can cause any residual humidity to expand and cause a bubble in the laminate. Cold roller mounting is a safer bet.
I suggest gator board because it will stay flatter over time. You are effectively sealing off one side of the mount board, so any changes in the environment are going to have a greater effect on the back of the mount, potentially causing cupping and/or bowing. Adding a laminate sheet to the back of the mount would negate this effect.