I have moved my regular BP before but that is when he was about 4 years old and only for about 20 min.

We are about to get another BP

Albino Yellow Belly by closhusan, on Flickr

but she is only about 3 months and we are moving her in winter and trip should be about 3 hours. Is bagging her and putting her in a small container necessary?

Here is what I had planned...let me know if this is okay....

Transporting in a small cage that I used for crickets when I had a chameleon. Cage is plastic with secure lid and ventilation.

I plan on heating a small heat pad and wrapping it in towels so there is no direct contact with the heating pad.
I was going to put a separate towel in a pouch shape under a small hide for her to coil up in.

Since I don't think that the heat pad is going to last three hours, I was going to get one of those portable hand warmers to swap out when I break (or when the first heat pad gets cold).

Let me know.