Dumerils, Hog Island, or small BCI (MALES - females of either species would get too large) would do alright in a 41 qt tub. The BCI may need something bigger as an adult though. But the husbandry of any of these guys is about the same as a BP.
Tarahumara mountain boas can do well in 41 qt tubs, but generally like slightly cooler temps.
Blood pythons or rainbow boas are options. Bloods may be too large and BRBs need higher humidity, but smaller bloods might do fine and you can up the humidity enough for a BRB by putting damp sphagum moss in the tub.
I keep young boas in the same rack with my balls. They move to their 4x2x2 ft enclosures when they outgrow the 41 qt tubs.
BUT!!!! Try Angolan pythons!! They are only slightly bigger than balls and are AMAZING snakes to work with! Same care requirements as balls and they do great in racks! 41 qt is all they'll ever need.......
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