20L for a 18" baby

Hello i might go ahead and setup the 20L for the baby instead of that sweater box. What do you suggest i use for heat? can i use a infered heat bub what watt? also how many keep babies in screen tops do they rub there nose alot? and how should i set this 20L up for my BCI

You're baby will be stressed out by all that room. Baby snakes are prey for many things... and with all that space above him, he'll feel completely exposed and vulnerable. That said, if you still want to go ahead and set up the 20L, I would put a TON of hides in there, as well as a few climbing branches and vines... that way he'll feel like he can hide no matter where he goes in the enclosure.

but the screen how do i keep the snake from nose rub? i plan on putting alot of hides and greenery in with it. SO should i go with the infered heat bulb? what watt would i need

I wouldn't go with a bulb at all. I'd use UTH for a RTB, they are extremely vulnerable to low humidity and don't do well at all in it. Bulbs suck up all the moisture in the setup, especially heat bulbs.