Don't worry about it...the joint between the tub and the tiled walls should be caulked anyways. Most manufacturers specify supporting the edges of the tub with a ledger board and bedding them in mortar so they are quite sturdy if installed that way. If you don't like the look of caulk, www.schltuer.com and others make trim pieces that are flexible that take the place of caulk at corners and changes of plane (look at Dilex profiles). Put it together right, and it isn't a problem. Avoid the steel tubs, it doesn't take much to damage or dent them, and then they rust.