Pretty interesting videos
Makes me want to make a sub robot to, but where I live ( Belgium) there's no clear whater anywhere...
So that makes it kindof not worth the effort.
Because you couldn't see a thing with camera's.
Anyway, most hobbyist will make a sub robot out of PVC pipes. I've seen a few made in an H form, with two propellers in the two lower ends of the H, and two headlights in the upper ends of the H. The camera was in the center.
Although it's not aerodynamic i think this is the best way to go as a hobbyist.