D is for Defense

First and Foremost, the main problem we have essentially is that we as Horde camp in the East workshop, more commonly known as Sunken Ring. Think of it like this, on offense horde portals in and runs straight from the west, thru the West Workshop, and to the front gate of the keep. Alliance would be foolish to wait at West Workshop because they would get trampled and mowed down giving us ranks. So why, on defense, do we do this at Sunken Ring? If Horde wait at Sunken ring and try to take it during the beginning of the fight, all it does is let Alliance get ranks and therefore siege engines. DONT TRY TO TAKE SUNKEN RINGUNTIL LATER ON IN THE FIGHT. Now that that is cleared up, maybe Alliance won't have insta-siege and we stand a chance to win.
The next thing we need to do is organize and prepare, pre-fight. Get into WG 5-10min before it starts so that you will have ample time to mobilize with the rest of your group. We will need to have some people stay in the keep and guard the cannons to keep some Alliance at bay and their catapults in low numbers. I would suggest 20-30 people. Another group will need to start out in Westpark Workshop, this group will need to be 20 people and 20 people only. Before the battle begins someone must designate for 2 people and 2 people only to kill the NPC guards as the guards only give rank credit to the killing blow. There are NPCs at both Westpark and Eastpark workshops. Also, someone will need to assign 4 people to stay at Westpark and for 3 people to head north to take West workshop. As soon as the battle begins the rest of the group will take off and hit Eastpark which is where there should be some Alliance, enough to get rank for most of the group that's there. After the alliance is gone, the group should get a few catapults and start to take out the East Tower and then head back west and take down the rest of the towers. While all that is going on and then initial rush of alliance have taken over East workshop and have now started struggling to take down a wall or a gate with just a few catapults, another group should rush into the East workshop and take out the alliance there and cap all the workshops, leaving the alliance with only 4 vehicles. This is the tricky part however, you don't want to rush the East workshop too soon as there will still be too many alliance there defending it. After all the other shops have been taken this should shake them up enough that they disperse out to try to recapture the lost shops.
The final battle will be at the Keep so after the Shops have been taken most of us can head back in and make as many siege or demolishers as possible and where ever alliance is trying to get in, that is where we will position them to take them out and they struggle to get inside.

As far as I know, this is a pretty good strategy and should work fairly well if we can get enough people to join in and follow orders.