I have a 20 gallon long tank with a screen top. I am having trouble keeping the temps in the tank up. I have a heat lamp on the warm side and an under tank heating pad in that end too.The warm end is around 80-82. I have put a towel on the top of the cool end to trap some heat but i cant get it past 72 degrees. The humidity is good at around 65. The room temp is kind of cool. Can anyone give me some suggestions to help with my problem?

Thanks,
Alex