For the eye cup you need to make a little rigid collar to go over the camera side of the eye cup.
The problem is that the eye cup is made of nice comfy soft rubber.
This soft rubber is not tight enough where it fits over the camera.
I found a nylon casket ring that fitted over it nice and snug. Tricky to get on, but once there it did not move.
It was my friends camera and it's still on a year later.
Nylon o ring/gasket thingy like this, but bigger and slimmer.