Reply #2: They make a tub and tile caulk.

[Ress1]

It's available in any hardware store in clear and white. It's a rubber based caulk which "gives" to prevent the shifting problem you mentioned, but it also waterproofs the seam you are filling. Caulk can give you a good finished look if you are careful during aplication. Keep a wet cloth handy to wipe away excesses during application. Practice a little before applying if you haven't done it before. Try not to over caulk which can get messy.Neatness and covering the seam are your main goals. Good luck, it's easier than you think.