I am currently trying to develop a ROV.
As I have neither a lathe or a mill but I have a 3d printer (an XYZprinting) I have try to do a pressure hull in 3d printed ABS.
After few months of effort I have finally a working prototype which has been tested up to 10 bars!
The main trick is to use epoxy resin to waterproof your parts.
I have done a video to share the process with everybody because as far as I am aware it is quite new:
I hope I will be able to work on the project and have a full hull soon!