This may or may not be a factor in your situation, but you said he is nearing a year old. I recently went through a 4 week refusal period with my guy (which I never did fully figure out the reason behind) and he was exhibiting some of the same behaviors you mentioned. What stood out to me in particular was that you said he seems more concerned with coming out and exploring than eating. This is exactly what my guy was doing. Normally he would have his head poking out of his hide at feeding time and I could just dangle the rat and he would nail it. During his refusal period he would wake up and immediately start climbing the walls (literally). He seemed so focused on wandering the tank that even when I had a rat right in front of him he would pay no attention, even slithering directly over the top of it to get to the other side of his tank at times. He would also immediately start to try to slither up my arm or out of the enclosure when I reached in to feed him. Someone on here suggested it may be breeding behavior. It is not uncommon for ball pythons to go off feed during breeding season. This person pointed out that even though technically it is not breeding season right now, in the wild they rely on temperature cues (how low the temps get at night for instance) to know when it is breeding season. Since we keep them at stable temps in captivity they have no good cues to judge by and pretty much make their best guess and start looking for a mate almost at random, but often around 1 year of age (though this varies some). If there was a cold front recently or for some reason his temps in the tank changed right before this started it could have something to do with it.

That being said, I would definitely keep the belly heat. Kudos on use of a thermostat, love seeing responsible and well educated keepers! Also it is wise to cover the 3 sides of the tank, simply because you can never have too much security for them and you may as well rule it out as a reason. Your snake will thank you for the added privacy. Like I said, I don't know what did it for my guy. I just kept offering each week and sure enough after about a month and a shed he ate and has been going strong ever since. It may well have been a breeding/hormonal thing though. One other tip, as strange as it sounds, you could try dipping the rats head in tuna juice before blow drying it. Sometimes the added scent will provoke a stronger feeding response. I did have some difficulty with my guy shortly after getting him home. I used the tried the tuna juice scenting just on the off chance that it might make a difference and it sure seemed to get him eating steadily. It may have been a coincidence, but I have heard a few different people confirm success with this method. If you have some canned tuna (in water) lying around, try draining the juice into a cup or ziplock bag and use it to scent it next time you feed. Who knows, it may help.