Which components for flat waterproof buttons controller
Unless you have designed and tested an IP67 or IP68 enclosure before, moisture has a way of getting thru plastic seals with vapour pressure and many plastic coatings are hydroscopic.  Neoprene and rubber are good gaskets for covering the  entire keyboard board and double O-ring seals are commonly used in compression cases.

These are some design criteria to keep in mind.

 To be waterproof, a membrane switch must:   
•   Be completely water resistant even in full submersion.  
•   Utilize an edge gasket between the overlay edge and mounting case.  
•   Be durable enough to ensure longevity.   
•   Use specific materials that prevent damage from extreme weather or temperatures.  
•   Have circuits and wire entry vapour pressure isolated from outside environments.   
•   Be simple to install or retrofit into existing equipment.