New ivory millipede enclosure. Temperature?

So excited for my ivories to come. Letting the tank settle before they arrive. 15 gallon with my custom soil mixture (all safe ingredients). The only issue I have so far is temperature. I live on Maine, so its cold. My small heat bad on the back isn’t adding enough heat. Sits at 65° with high humidity. I ordered a larger heat pad, so hopefully that will help. What temperatures do y’all typically use for ivories?