I have a subal megadome for sale. its about an 11inch dome with the conical back originally designed for the 14-24 but works really nicely with the 16-35 with appropriate extension rings. Its a subal type 4 mount but I have been using it with a nauticam converter without any problems. It was some absurd amount new. There are no scratches on the glass and in comes with a slightly tatty home made neoprene cover .
Asking £800 for the dome and converter. Its currently in Brighton in the UK but im between there and the midlands so could bring it up. Happy to ship at cost to wherever.