Hi! First post here. I did search this before posting, but I am sure I've missed something somewhere. Apologies in advance for that. I'll preface my questions with some background and setup info.

I have a very healthy Petco (I know, I know) BP that I've had for around 3 weeks. It is 110g right now, it has shed cleanly once, and is eating regularly and vigorously every 5 days- doing very well from what I see. It's very calm and easy to handle. I'm really happy with him/her. I've set up my 20g Long according to some of the guides I see here. I have a tstat controlled 12x8 UTH on the warm side which gives me a glass temp of about 93, and the surface of the cocofiber substrate on that side is right at 90-91. Ambient in the tank is 80 or so, and substrate temps on the cool side are around 77. House ambient is about 73. I have a foil wrapped screen lid with a cutout for a central heat lamp, I've done this in an effort to keep humidity under control. I can mist and cover the tank, sending humidity up to 70-75, but it slowly creeps back to the mid-upper 40s over the course of a few hours when it's cold out and the heater in the house runs a lot. I don't mind misting and wetting/stirring the substrate when I am home, but I don't like the swings in humidity when I am gone at work or when I leave for a bit (going out of state for Thanksgiving for 2 days next week).

Clearly my setup isn't going to work long-term here over the winter although it will be fine in the summer I'm sure. Rather than ask about what else I can do to keep humidity up, I'd rather go in a different direction- I want to get an animal plastics enclosure next month, which leads to my questions-

How do you think short term humidity drops to the mid 40s when I'm at work or gone for a day or two will affect my animal? Or, in general, the inconsistent levels?

Is it worth it to go to an AP cage for a baby who will outgrow it? If it's worth it, what size for a baby? From what I see, even their smallest models are on the large size for a BP the size of mine. I've thought about getting a T8 and putting in a temporary divider to give it a smaller space for now. I've also thought about just going to a small clear tub for a while, maybe even for the winter to help maintain constant humidity, or maybe full time until my BP is big enough for a decent sized AP cage- but with my home's ambient, I'd be wrestling with heat as opposed to humidity. A tub certainly would be the least expensive option.

Clearly the 20G Long isn't working out for me, so what do you suggest? Thanks for your time. This place has been invaluable to me so far.