With respect to the original post on this thread, if I read what you are setting up I think you are mixing and matching two different ways of doing things.
The Zeroshell “net balancing” and failover is working at the IP level while interface bonding is working at the ethernet packet level.
In my opinion, the Zeroshell net balancing feature is more useful if you have multiple ISPs and wish to distribute traffic between them and are unable to use the bonded interface approach.
In your case you have a single data center you are connecting to so you can use the bonded interface approach.
Your data center setup sounds reasonable to me. On the remote side, I’d forget about “net balancing” and setup three VPNs one on each of your three links and then bond those into one gateway interface. I think the VPN interfaces may need to be on the same subnet.. Been a while and I don’t remember the restrictions on bonding. Your routing is easy: The bonded interface is your gateway.
The Linux bonding driver has a bunch of options and it has been a while since I used them and I’ve never done it on Zeroshell. But I recall that there are options for load balancing and for fail over using the bonding interface, so that is where you want to focus.