The S1-200 controller is built robustly. However, to ensure your equipment lasts as long as possible, install it in a place where it is protected from the elements.
The controller has an IP68 rating. While this means that the controller is well able to handle water, it is still advisable to keep it out of rain.
A good place to mount the controller is beneath the solar module.
Read this article for more information about mounting the controller: