Main Camera view in a specific region of the player view

I’m trying to show the main camera view in a specific region of the players view.

Think picture in picture but the “first picture” being blank/blank. I’ve achieved this already using a render to texture but I’m concerned it maybe more resource consuming that it needs to be. I only need 1 camera view but it doesn’t need to take up the whole area just a small box. I do need to turn the camera off and on, which I’ve achieved with the render to texture but just changing the targeted texture/material in the HUD.