Expansion Chambers

I am installing a new shower valve. Should I install expansion chambers on the hot and cold 1/2 copper water lines near the valve?

A shower usually doesn't need it, and if it does, expansion chambers are old school, and never worked very well for long - they quickly become waterlogged and are often impossible to recharge. If you need hammer arresters, put in the real thing. Sioux Chief and others make them. these are either a bladder or a sealed piston chamber that will stay dry and working for many years. Think finger over the end of a straw...once full of water, the end stays capped, they rarely drain and thus are useless.

Piston type can also fail or respond slowly when the "O" ring seals start to stick. A bellows is the one which will last the longest, but the bellows can also fail if the "folds" develop metal fatigue. Therefore, any mechanical one should have provision for accessing it for replacement purposes.