I mostly agree here. I actually have a huge dislike of tubs purely for aesthetic reasons, but both of my rainbows are in tubs until they are big enough for a large PVC enclosure. Rainbows - like any species - CAN be kept well in a glass tank, but it takes a lot more effort and you really have to have it set up perfectly and regulated on point. If it isn't, the animal suffers. It sounds like OP's setup isn't ideal, but if they want to keep the glass, they need to be able to be constantly adding humidity - misting once or twice a day will not be enough. Ultimately, imo, it doesn't matter what the snake is kept in as long as its needs are met and if they aren't something needs to change, like in the OP.
I was going to suggest switching to a tub but it doesn't sound like OP has a good method to heat a tub and can't afford to get a tub safe heat panel. I'm skeptical that a CHE in the method I described will warm a larger tub.