As long as I've taken us off sailing all together, this roof top deck has been one of my biggest building challenges. My first one didn't last long(15 years) In hindsight, I went at it all wrong. I tried to keep water out at the ballustrade railing and trim(and sealed below with copious amounts of bitchethene). I found out this area is in extreme weather and water found it's way in. The first sign was the railing began to rot. But that didn't show water ingress below. Some repairs later,...

This second attempt is different. With a new EPBM pan running up the sides of the curb, I made my water stop there-a custom aluminum cap flashing. It extends down over the EPDM on the inside, and down over plastic wood-with no seams for water ingress-on the exterior.

The new railing, cut from pressure treated stock, simply rests on top of the aluminum extrusion. There are no holes, in fact only it's weight holds it in place(I may tie it down if a hurricane comes close ) So far it's working perfectly except that as you noticed, the top of the railing doesn't hold paint for long. I may have another white aluminum piece bent to just cover the top with a drip edge bent to channel rain away a bit? But it's pressure treated so I decided to defer painting it, another year,.....