the XM GXM-30 antenna is simply magnetic with no mounting hardware included.
I used a scrap piece of steel measuring 3.5"x5".
You can see the pattern below in the first photo.
The only step requiring any accuracy is placement of
the four screws holes.
Then it simply clamps in between the Zumo cradle and the Ram mount.
 |
 |
|
 |
 |
|
 |
 |
|