Looks pretty good! There are a couple things that need changed, but I'll let other people pitch in. I don't want to call out something you're doing right!
As for plastic+heat, Idk. My cresties have no UTH so I'm not sure how that would work on a tub. Not much to say, I'm notorious for having bad husbandry (lol); I don't wanna give you wrong advice. Someone said it may be the season, which is a good thing to consider! My boy is fasting right now, it's been about a month. Maybe Asriel is doing the same. Good Luck!