the Camera Frustum is not defined as vectors directly, it is defined as 6 semi-tangible planes connected to the camera.
depending on what you need to do you might find some of this thread of interest
might also want to look at post 14 for a blueprint method as well.
if you need to figure out if something is being rendered at all there are some “easier” and less exacting methods the doing full frustum calculations, with WasRecentlyRendered()
or doing a projection from say the mouse pointer, or the forward vector of the camera.