For most of the year, no you would not need a heating pad. As long as the bins temps stay in the 85F-95F range your good. Watch that it doesn't get too hot though. In the cooler months, yes use the heating pad to maintain those temps. You also want to keep the humidity levels up in the bins (the water gel helps do this as well as provide a drink for them) if the weather is dry and hot, use a larger bowl of the water gel, the more wet, gel crystals, the more humidity. Also, adding sliced fruit also helps provide moisture/humidity. Oranges and apples work great.
You can get the crystals online from any of the roach vendors, or at a lawn and garden center and some Walmarts carry it pretty cheap. A 1LB jar will last a LONG time. It is cheaper to get it by the jar/bag than to get a few oz online though.