Take most of the care sheets online with a grain of salt. Basically anyone can write these things, and even those from reputable sources can be outdated. I have seen many a care sheet from Reptiles Magazine be blatantly incorrect. GTPs are definitely not the hardiest of snakes, but with recent advancements in caging materials and heating devices, their care is much more manageable.

Basically if you can keep the ambient temp correct, and the proper humidity levels, there isn't any reason why they wont thrive.

Just to let you know, a 12" high cage will do great for a hatchling, and up to a couple years of age. Once the baby is older an 18" high cage is more appropriate. People make too big a deal out of the vertical gradient/space for GTPs. It is actually the horizontal space that matters more. Many top GTP keepers have noticed that their snakes do not frequently 'bask' with a heating element on the top of the cage, and instead mount heating devices on the side of the enclosure to allow for a horizontal gradient amongst the perches.