If you can access underneath the false bottom, put good quality (eheim,fluval) adjustable aquarium heater suction cupped to the bottom. As long as the water level is above the heater, you're good. It will heat the water and work like your radiators, heating the air in the tank. Just don't skimp on the heater
. Like i said, you want it to be adjustable, those preset heaters are garbage and burn out quickly. Otherwise, you can use a heat emitter as long as the top isn't glass, or relocate the enclosure to a warmer, upper floor of you home for the winter. All my tanks, both planted and frog, run aquarium heaters in them since they are in an unfinished basement with no heat and i have yet to have a problem. It was cold here last night. My basement was 60 degrees this morning, but my white's tank was 81.2 degrees/82% humidity. Hope that helps