I don't keep Gila's so I won't give you specific temps ect, hopefully someone will help you out there. If not, I'd use what is recommended for species native to the same area.
As far as desert species in general however, I prefer overhead heat, UVB lights, and a dry enclosure. The overhead heat helps keep a dry environment. The humidity I concentrate in the hide area to simulate what happens in the wild. While there will always be a temp range prefered, I also like to have a basking spot that exceeds this, but only recommend this with a larger enclosure. (Don't want to cook anybody
)
I hope my viewpoint helps, however vague it is.