A heat lamp or a ceramic heat emitter will help bump the cool side temps where they should be, as that is a little too low for them. Whatever option you go with, just make sure the watts of the lamp/heat emitter don't exceed the max of your thermostat when combined with your undertank heater. By that I mean if your thermostat is rated to handle 500 watts and your UTH is 120 watts and you get a 150 watt heat emitter, you'd obviously be below the threshold limit for your thermostat, if that makes sense. I know some people use UTH's on both sides of the tank, with the cool side hooked to a separate thermostat that's set to a lower temp than the warm side. The heat lamp or heat emitter will both kill your humidity, so just so you know. Good luck!