I appreciate the replies.
Yes it will be a joint bath/shower. I was planning to just put a curtain rod up that would go the length of the tub/bench.
My plan was to do cement backerboard and then a waterproof membrane. Unfortunately, Kerdi is not available in Canada yet (as I was told at Lowe's last week). That was how I planned to do the shower after seeing it on DIY Disaster
Just so I understand you are both recommending that I skip the bench idea and frame a wall that ends at the tub/shower so it is fully enclosed by 3 walls. The reaming space between the new wall and the existing wall will be 9 inches or so depending on framing. Not a very wide storage area...but I guess it would work just with some open shelving?
The bench is the only thing I am stressing about for this entire project so maybe I should just take it out and do the wall. That would save me from any problems in the future as you say.