Tank internals. The black stuff around the edge is a thin rubber or silicone sheet with adhesive backing.
I wanted a way to access the tank without removing the roof plate so I stole a screw top off a juice or milk carton and made some holes.
Hot glued on the inside of the tank lid.
Very low profile, but just enough grip to unscrew it.
It will be hidden below one of the tank inspection hatches.
I had to do a lot of guesstimation as I don't have any good direct reference shots, but the end result is passable from a distance. (Top left is the model, the rest are all the reference material I have.
