I don't know about other types of tubes, but surely CRTs are DESIGNED for horizontal applications.
I'm not sure they're designed one way or the other. I've seen 'scopes mounted both ways, as well as computer monitors, radar screens, and video monitors.
But, of course, if you mount them screen down then the electrons fall out onto the floor. Fuller Brush used to make an electron broom, but I think they're discontinued.
