Hi there, I'm a bit late to this thread...
My GTP is coming home soon, and for the last month I've read extensively about their needs, husbandry, etc. on several forums and all the care sheets I could find...
I noticed in your post you mentioned a "20 gallon tank" (guessing that's a glass open top fish tank?) and heat lamps.
From what I've read and heard recommended from quite a few breeders with a lot of experience this is not quite ideal. Most recommend a closed top enclosure with doors at the front. This will keep the heat and humidity in the enclosure, and aid in your ability to handle the animal - approach from above is trouble because your hand will be seen as a predator. If you enter from the front, remove the snake with the perch, then the animal can move onto you with much less stress and fear/aggression. Tangent there, but I guess it sorta applies..
For heat many people recommend radiant heat panels or flexwatt...but lamps and CHEs are used as well.
Hope that helps if you haven't already sorted things out