I would bring an ice chest or styro-foam shipping box to transport the boxed/bagged snake in safely, just to make sure he's not exposed to excess heat or chill,
& regardless of season. Sun coming thru car windows & heat from engines have killed snakes before...remember they are trapped & cannot even holler for help.
I agree with bcr229's post- by all means check out the snake first. It's rare but I've been to a breeder's house many years ago to pick up my hatchlings...a large
& well-known breeder att (& very social & funny guy too).
Looking forward to seeing your new BCI...great pets!