Stainless steel screws would be the best choice.

A stainless steel, corrosion-resistant screw that promises strength and durability.

A screw is a fastener that has a ridge or thread encircling the entire length of the device, whereas a bolt has a threaded end and a smooth shaft.

Stainless steel screws are most commonly used when reliable weather, water and corrosion resistance are required.

Stainless steel screws are usually stronger than zinc screws. Zinc screws also rust more easily.