You would still need a radiator and fan, it will just be larger and more bulky, less effecient, and shaped like a resevior.
You are still thinking inside the box my man
Move that peltier directly to the cpu and you will have far better cooling. Anyways, why not just get a large passive radiator?
Oh, and you may end up heating the system up with pelts because the cold side can only be as cold as the hot side is cold.
Plus, tecs use LOTS of power and really the added complexity, the decrease in performance, the problems with condensation, possibly added noise (you will need a very large power supply for multiple tecs, possibly requiring a fan anyways), and not to mention the added money just arent worth it.
A copper box will not absorb the heat from the water very quickly anyways, there just isnt enough surface area.
A radiator is really the easiest way to go.