So I went to go feed my young ball python tonight and found him dead and want to know what went wrong?

I'm a first time ball python owner and got a hatchling from LLL Reptile back in mid March. Everything was fine up until the beginning of last week when I noticed some mucus coming out of his nose and mouth and a popping noise happening everytime he breathed so I called and made a vet appointment immediately. The vet told me he likely did have an RI and to give him .03 mLs of enrofloxacin a day orally which I've been doing. She also said he was just sick and it didn't seem like anything was fatal yet (this was last Thursday the 22nd). Today marks four weeks from the last time he ate so apparently he hasn't been feeling good for a while (I was feeding him small frozen-thawed mice, the size above pinkies, once every five days).

It's my fault for setting something in his tank up wrong, but where did I go wrong? I thought I did all the research in the world and then some before getting him. =( He was in a rubber bin about a foot and eight inches long and about a foot wide with plenty of holes in it, around the same number of holes that were in the rubber tank tutorial on this website. It also had a snap-on lid. The vet said I should get rid of it and put a screen or something on top so he gets more airflow but I've never seen anyone on here do this with a rubber bin...? Did my snake really just not have enough ventilation? It might be worth noting that the tank is also taller than most rubber bins that people keep their ball pythons in. His tank is around a foot tall maybe?

As far as heating stuff goes I have two UTHs attached to thermostats on different sides of the tank. One was at around 80-82 and the other around 90-92. I had no heating lamp but from what I read they don't really need one, correct? That's why he had two UTHs, to make sure one side was always around 80 even if my bedroom temp (where the tank is) dropped slightly. It's always at 78-80 degrees, and it ~occassionally~ drops to 76 but not often but that doesn't seem like it would be a major issue, or would it? The humidity was always from 50-60%, occassionally higher but I took the water bowl out when that happened. For reference I was using the usual thermometer/hygrometer recommended here from Walmart that displays two temperatures and the humidity; I had the thermometer probe right on top of the heating pad inside the tank. He had a hide on each side of the tank and I was using aspen until the vet told me aspen can potentially cause respiratory issues due to its smell so paper towels were used instead.

Over the past few days I noticed him hanging off his hides at weird angles and not really moving around much. Were his conditions too cold and/or did his tank basically suffocate him to death with stagnant air? These are the things the vet suggested I change but what should I change them to? Should plastic lids really be ditched?

Thanks to any suggestions any of you might have. Poor little guy. =( It's a little heart breaking to deal with, not sure if getting another one is likely but if so I don't want this to happen again.