In the Unity Forums, there is a nice tank C&C community project. You could try and integrate some of that (I think it was in the Collaboration section.)

var CamSpeed = 1.00;
var GUIsize = 25;

function Update () {
var recdown = Rect (0, 0, Screen.width, GUIsize);
var recup = Rect (0, Screen.height-GUIsize, Screen.width, GUIsize);
var recleft = Rect (0, 0, GUIsize, Screen.height);
var recright = Rect (Screen.width-GUIsize, 0, GUIsize, Screen.height);

    if (recdown.Contains(Input.mousePosition))
        transform.Translate(0, 0, -CamSpeed, Space.World);

    if (recup.Contains(Input.mousePosition))
        transform.Translate(0, 0, CamSpeed, Space.World);

    if (recleft.Contains(Input.mousePosition))
        transform.Translate(-CamSpeed, 0, 0, Space.World);

    if (recright.Contains(Input.mousePosition))
        transform.Translate(CamSpeed, 0, 0, Space.World);
}

when I was doing an RTS type game before I made this script for my camera so maybe it will help you.

It creates a non-visible rectangle on the side of the screen with an inset of 25 (var called GUIsize) when the mouse enters these areas it moves the camera in world coordinates (I made it world coordinates as my camera was angled at about 45 degrees like the total war games if you've ever played them)

You can change the cam speed to alter the speed of the cameras movement

Hope it helps you

Scribe