K40 Water Cooling Mount

This is a mount for a water cooling system. The pump is a 22W 800L/H china pump with a small water reservoir. To cool the laser a bigger container or a chiller must be connected in series. The whole mount is screwed with two screws from the inside to the side of the K40.
My experience: Don't use chiller! The temperature can't be cooled enough. (I used 4x 120mm fans). The biggest problem is bimetal corrosion. Especially when you cut only a view times a month.
I empty the whole system after usage. Do you have recommendations for me, how to solve the corrosion problem during longer storage periods?