Actually, the brackets we made look kinda like this, with the triangle representing the "christmas tree clip"
∆
_l¯l_
This allows you to fiberglass the ends to the back of the door easily, meaning you won't have any exposed screws.
Also, any reason you don't want to mount the vin close to the where it originally was? I know some states like California, for example, are really picky about this, and technically I don't think you're supposed to tamper with, or remove the vin from its original location. This is what we did, and it doesn't look bad:
Matt