I am remodeling/expanding my downstairs bathroom to add a tub/shower. It's a small space, so I plan to install a 4.5' tub. I will need to build the plumbing wall for the tub; however, because of space constraints, I would like to build a 2x3 wall. Can I fit the necessary plumbing for the tub/shower in a 2x3 wall? Or is 2x4 - or even 2x6 - the minimum?