Need advice on my ratsnake!

Hi there, I have a (approximately we think over at least 10 years old) five-foot rat snake that I just cannot seem to make happy. He is currently in a 3-foot vivarium (we have his upgrade already, just waiting on the sealant to dry), it's got a temperature gradient of approx 28°C - 22°C, a basking temp around 30/31 and a humidity around 53%, with a bowl large enough for him to soak in. Nighttime temp goes down to about 23/21°C. He has always had problems with shedding and eating. I've tried moss boxes, baths, leaving him completely alone, he just will not shed, his last shed was the 28th of March. He goes up to 3 months without eating occasionally, despite offering him every week. Most of the time we have had him he has been quite inactive, we have given climbing room and he stays in his hide for months. A couple of months ago I upped the frequency of handling to encourage him to use his muscles because his grip was starting to feel a bit weak. Since then, he's been constantly active at a rate I've never seen, he is constantly moving around, climbing and rubbing his nose on the glass, if I try to let him out he will slink back and hide. He is also super aggressive and always has been, we got him from a rescue in 2021 and they said the same, but I'm worried that it's stress from illness or something. At the moment he hasn't eaten since early December. I am taking him to the vet, but I am quite used to a lot of vets not actually knowing what to do so preemptively I'm coming here. Just not sure if this is normal for rat snakes or I'm missing something major, has anyone else had this experience? I've included a pic of his enclosure with a kind of anatomical breakdown to try and show what's in it because it's not easy to tell from one picture the way it's set up. Thank you for any advice. Also his scales recently sound a bit crunchy, which I am very concerned about.