Camera in UI

Hi,

With Unity 5.1.0, I want to create an UI, with a new UI system, and in a Panel, I want to display a 3D view, resulting from a camera output.

It works in Editor mode, but not in running mode.

In details :
- I have created an UI system (Canvas, Panels, buttons, ...)
- in one panel, I have added a box,
- the box is texturing with a Render Texture,
- and the render texture is assigned to a camera of mine.

In Editor mode, I see the camera output onto the box, but in running mode, no box, no texture. Nothing...

Any idea ?
Is it the right way ?

Sylvain