I am trying to decide how i should make my hatch rims on my Nomad (Design by Björn Thomasson). I will probably make them out of plywood. I seems like most people use 3 or 4 mm plywood for the rims. But I can't find anything thinner than 6 mm locally. Is that too thick?
I am especially worried about the spacer. If I use a 6 mm spacer I guess I will have to use a gasket about twice that thickness = 12 mm.

I have also considered to use some hardboard aka "Masonite", which is 3,2 mm thick. It doesn't work well with water, but since it will be covered in glass I suppose it doesn't matter.