Hi Josh,
Thank you for posting your question as it has helped me also. Your vivarium is the exact same one that I was sold for my blonde spotted python! He is a bit over 7 months now and I have been having the same problems as you with heat retention even in the Brissie autumn weather! I have a 100w heat lamp and recently purchased a heat mat which has helped a bit. Under belly heat in warm end 29.8 and air temperature is 28.9 warm end, 26.4 cool end at 7.30pm. Basking temp on his branch under the lamp is at 32 C, but he has to climb for that and yes he does get up at night when he chooses. Last night for the first time after his dinner and under his own volition, he went to his other hide at the cool end of his house for a cool down. Tonight I have laid a towel over some of the mesh at the top. Our house is a cold house, all tiles and glass doors that stay partlly open onto a deck, other pets come in and out during the night. Thinking of getting a 150w heat lamp for when the weather gets cooler, or move the vivarium to a smaller room that has carpet and I can close the door... any comments and suggestions would be helpful. Thanks again Josh, and everyone who posted.