I've read that boas often eat the slugs, it's probably a good source of nourishment for them and in nature might be so as to not attract scavengers. Can't say for sure if they all do it though, this was my first clutch of boas. I've bred many colubrid snakes and Ball pythons but these were a first.
I don't have any BCI, they of course stay smaller and require a higher humidity level. Beyond that you should contact some others that are more experienced. russ lockenwitz, RioBravoReptiles, and Jeff Clark are some of the names I follow on this forum and seem very knowledgable (I'm sure there are more).