While there are various examples of cargo bikes having been designed on BikeCAD here, I don't feel comfortable claiming that BikeCAD is a particularly good tool for designing these types of bikes. There is no functionality specifically intended for designing bakfiets for example. However that has not stopped some designers from getting really creative with the tool and making some pretty good representations of these bikes. I am open to adding more features to support this style of bike in a future update. Thanks for letting me know of your interest.