The tank is probably too big for one so he feels overwhelmed and nervous. Either get him a smaller tank/tub or make that one really crowded with stuff so the snake feels like it has some security.
Side mounted UTH is pretty much pointless, unless your snake has somehow figured out how to stick to the side and absorb the heat. You should peel it off while it is warm (but unplugged) and reapply it to one end of the tank on the bottom. You should also get a thermostat and attach the UTH to it to help get the temps right. UTH's from what I know of them basically just start heating up and don't stop until they reach their max temps which can be far, far too hot. A thermostat will help you regulate this. You can pick a cheap one up for about $30.00.
The ceramic heat emitter isn't doing anything except sucking up humidity (which by the way at 45-50% is barely cutting it as it is). Get rid of the CHE. Ball pythons need belly heat, not overhead heat. If you want overhead heat get a 60 or 75 watt red night light. It'll give you both viewing opportunities when it is active as well as some heat. Just getting rid of the CHE will do wonders as far as humidity goes. The red light will kill it some, but not to the extent the che is.
Try to get your temps to be 88-92 on the "hot end" and a general ambient air temp of 80-85 elsewhere in the tank. It might take some messing with over time to get the temps right and to get your humidity between 50-60%.
Put hides on both ends of the tank. Don't make the snake choose between feeling secure or thermo-regulating its temperature. Give it what it needs regardless of what it wants to do.
Also try covering the top with foil to help trap the humidity in the tank. If you've got a mesh screen on there a lot of moisture is slipping out through that screen.
Finally get some black construction paper and wrap it around his tank and cover all of the sides (I'd leave a maybe 1/8 of one side without covering so the snake isn't totally "in the dark" and you can check in on him). Try to leave him completely alone for a week or two except for changing his water. See if that doesn't help him to feel more secure and less threatened.
All that being said I think the biggest issue could well be the size of the tank he is in and his inability to find security in it. I could be wrong, but 55 gallons is really big for a snake that is naturally acclimated to living in holes underground.