That's gonna be a BIG enclosure. Give it a try and see what happens but of course a much smaller box would be better. The extra hides should be enough to keep it feeling secure though.
A 41qt will be fine for a baby boa. In addition to the hides, you should also put a piece of wood or small aquarium decor in the tub for the snake to climb on. It is common, after they settle in, to perch on top of their hides or other available furnishings.