Some discussion about these lately, I have this installed on a 2008 Z21. I ordered this from Van at BBT, very knowledgable guy and I highly recommend reaching out to him. The mount has a panel cover that came with the bracket, this replaced my old scratched up cover. On the actual mount there are two sizes available.. I ordered the larger of the two which has an inch wider spread between platforms than the smaller bracket (smaller won't work with HDS 10's or 12's).
On the actual mount, one side will be slightly higher than the other. With the angle of the panel and bracket most people have the top unit lower, so there is a set back.. but I prefer mine flush with each other, so I have the lower side in the front.
The mount itself is very stable and has no problem in rough water. Way better than RAM mounts and cheaper than 2 kong or similar type mounts.
Here are a couple photos.. I have more in dropbox that you can access:
https://www.dropbox.com/sh/0rnsf06iu...izJ9tXAua?dl=0