I would like to add that the vet opened the snake's mouth and showed me the "glottis" and showed that it was completely clear of bubbles of any kind, not even saliva bubbles. I would think that after this long a time, that if it were a mild case of RI it would at least show some bubbles?

I am currently keeping him 90F warm side, 82 cool side, with humidity ranging from 50 - 70%. Basically normal husbandry. I don't see anything wrong with how I am keeping him?