I would bump temps 1-2F on the hot side for now and try increasing humidity a little. The temp bump assumes he still has a cool side that's not more than 78F or so (and can be as low as 75F from what I understand - but I'll let some colubrid experts chime in here - I keep corns but not other colubrids). You can gently mist 1X a day and I would recommend getting a basic hydrometer. Not super accurate usually, but will give you an idea. You don't want it too humid, but probably a little more than it is now.
For what's it worth, depending one where you live, what heating/cooling system you have, etc. "room humidity" can vary a lot. Remember, RI's can be caused by stress and/or too much or too little humidity. I would research what he needs and make sure you are pretty close to slightly higher for now.
The fact that he is eating is a great sign. What makes you think he has an RI?
I had a false alarm with my BP a few years back. I moved and it was taking a little while to get humidity dialed in and it was a little low for a brief period. I heard her whistle a few times and got her to the vet the next day. By the time I got there, there was no whistling and she looked and sounded fine. Turns out she probably had something stuck in her nose like a piece of shed or dust.