First things first; water goes everywhere!! and that is exactly the thing you don't want to happen.
So sealing EVERYTHING is a must.
Placing the basin
We made an elevated floor where we would fit the shower basin. We needed it elevated so the drains could fit underneath. Once the floor was in we sealed it with a special rubber. Then placed the
basin and used silicon sealer to attach it and make it water tight.
For the walls we used the same stuff on the walls as in the rest of the van. Its called Vilon and It looks a bit like fake leather but thicker and gives it a soft feeling. Its water tight and
easy to clean. This is often used in boats.
The typical camper sinks are so plastic looking. So we decided to instal a normal stone sink. In this case a round one so It wouldn't take up to much space. With a pillar of wood underneath so we
could let all the drains and hoses run behind it.
The sink tap is also the shower head.