New Green Tree python and a question

[Joeyyb]

Hello everyone, I just joined the forum and I have a question. Yesterday I went to the White plains expo in new york. I picked up some food for the snakes and the crested, but while I was there I also picked up a baby green tree python! Now I have been doing research on them and the only issue is I didnt expect to get such a small one, so the 12x12x18 i had set up seems to big. So I put it in a shoebox tub I had that I put perches in a water bowl a fake vine and i have a heat mat on the bottom of the outside of the tub with the thermostat probe on it.
Now here lies the issue, i had bought a CHE for the 12x12x18. Now I have the temperature inside over the heat mat under tub to be on average 86 degrees that varies up and and down 2 degress. The heat mat is a small 4watt uth and I do not think it will get the ambient air temperature to be the proper degress.
I also have a regular 10 gallon that is not in use. Should i leave the gtp in the shoebox and go buy a higher watt uth and try to put it on the side of the shoebox or move it to the 12x12x18 or the 10 gallon? Ill post pics soon.