Sounds like a great idea for your tub chair. I made a sort of slipcover for my DH's (old, tacky, well-loved) recliner. I posted a picture on here then wrote a tutorial as I made a second one. It's in the Tutorials section. I think it's called Quilted Recliner Slipcover. Now I have another chair to cover and I'd love to see how your tub chair comes out. We're just about worn out the two I made for the recliner so if I still can't convince him to get a new chair, I'll be making a new one soon!
AnitaSt