You can also try a radiant heat panel on the roof of the pvc cage. I use a Pro Product one in my 4x2x1 Proline HDPE cage for my red tail boa and it works great. Keeps the humidity around 60ish and 90 hot side and low 80s cool side. Plus if you use something like a Herpstat, you wont use much electricity as it "throttles" down and only trickles in electricity as needed.