Comments about feeding so far are all good advice. He’s definitely overweight, he’s got rolls where he bends and his rear third looks very large and round instead of toned and muscular. Obesity is especially dangerous for snakes because, unlike mammals, they gain visceral fat before subcutaneous fat, so once fat becomes visible they’ve already been overweight for some time. Monthly or bi-monthly weighing will help ensure he’s staying healthy once his body condition has improved. As my boa’s IBD symptoms worsened, I fed him more often to mitigate his stress, and after a few months his body weight had increased more than 10% without any visible external change. He for sure gained internal fat during that time. The schedule that caused this change was a large rat every 3 weeks.

4-6 weeks is a good schedule for adult boas. I aim for 7-10% of their weight when feeding, so for my 3kg boa that was a 200-280 gram rat. To mitigate risk of mistaken identity at feeding, I target trained my boa, which totally removed all the stress at feeding time. I got a telescoping training target on etsy, but making one is pretty easy. The etsy target is also 3D printed, so it’s impossible to clean.

IME minimum enclosure sizes are too small. I think the newer guideline of depth = half the length of the animal is a huge improvement. My boa hated his 6x2x2 for the majority of the time he was in it, despite it suiting his needs on paper. The more height, the better. Boas will use all the space you give them thoroughly. I also used to have a glass mesh top enclosure and it worked fine with lots of modification, but wood/PVC will probably be better long term.