did you use PT lumber or just regular pine? Also its a good idea to use some kind of "air barrier" underlayement (housewrap) like they do on roofs and sheeting between the studs and ceramic board. That way moisture doesnt get "trapped" for the termites or soak your insulation. Especially true if your bathroom is on an exterior wall (bump the R value for this). Also I usually grout the cement board seams with concrete and try to cover the fastener heads. One thing Ive come to like is the ADA compliant shower pans that are flush with the finished floor. Looks so much cleaner. Not something that could be easily adapted in your situation.