Welcome! For Boas Constrictors (BCC, BCI etc.) I like 41qt racks. Once they're too big for those you'll need to move then to cages. If all of your boas are smaller localities (sorry, I'm not familiar with which ones are which size) you can get a rack that fits both 15 and 32 quart tubs so that when they're too large for the 32s they can move to cages as well. IMO animal plastics is the way to go for both racks and cages. Check the quick ship items on their webpage for 15/32 racks on sale for a darn good price.
Animal Plastics