Just a suggestion here so take it or leave it.
BNS gave you the best advice you can get for setting up a "baby" boa. Those methods were used by the pioneer boa importers/breeders in this country after years of trial and error. They work, folks like Vincent Russo and Gus Rentfro are names to be trusted and they would recommend exactly what BNS posted.
If you are not capable of duplicating those methods, consider a boa that is slightly older. My boa was 10 months old when I received him and I was able to put him in my HDPE (plastic) enclosure. He was not a baby, but he certainly wasn't big.
Size 10 shoe for reference.
Size in relation to his 4' x 2' x 14" HDPE cage.
Its' not a bad option if you are a little uncertain, or worried about a very young animal.
Food for thought.