The towers give the offense a bonus damage buff. As each tower goes down, part of the buff switches to the defense. The faster you burn the towers the better.
You do not need many people in the fort ... as long as they know how to use RPGs and communicate.
It's best to move as a group ... cap a workshop and destroy the towers from one side of the map to the other.
Leave a small defensive team at your southern workshop ... if you lose it, you have a long ride to get it back.
Cap the Northern WS Nearest Your FP
The enemy will come in at their fly point, and they will naturally zerg the nearby workshop. It will take them awhile to reach the other northern shop, however, which gives you time to cap and defend it.
With only one northern shop, the enemy can only come at you from one direction. This makes defense easier because you do not have to be watching two sides and moving back and forth.
Keeping the ws will reduce the number of vehicles that the enemy can build.
Sending troops to cap the ws will cost the enemy time ... and you can easily send reinforcements from the fort.
Keep the Rooms Clear
If the enemy controls a room, then they face no resistance when their tanks arrive. This means that they can knock down walls without taking damage, and it means that they can shoot at the door from long range.
Once you kill a group of incoming tanks, reinforce as needed and kill all of the enemy players in the room
Push out through the hole and establish a defensive perimeter. Do not get too far away from the fort ... the enemy may attack from a different direction.
Build Vehicles
Vehicles are amazingly useful on defense. In general, you want one or two in any room whose walls have been breached. You want the remainder to be outside the walls, supported by infantry, and watching for incoming vehicle attacks.
Long range cannon can kill enemy tanks before they reach the fort.
Ramming is effective against enemy tanks.
Catapults do solid AOE damage against infantry.
Use RPGs
These are your single best weapon against tanks. Everyone should have one and know how to use it.
RPGs are aoe weapons - one RPG can take out a whole stack of tanks
Don't fire RPGs at long range outside the fort ... they are only accurate at a close distance.
RPGs are very accurate inside the walls of the fort ... any tanks that get inside should immediately be hit with RPGs
RPGs have a slow casting time ... you may need to turn your character to keep the aim on line
With Tenacity
Short-handed defense is probably the most difficult task in WG. You need to form up into teams and use your superior health and damage to limit the enemy's zerg.
Go south first. As the towers go down, your damage will go up. In addition, you really need to shorten the game. Put a big team south and use a smaller team with RPGs to defend the fort.
Depend on RPGs. Even with your buff, RPGs are better at killing tanks. Every player in the fort should have an RPG.
Kill the zerg. The enemy will be trying to flood a room, gain control, and bring through a mass of tanks. You need to use your tenacity advantage to kill lots of enemy infantry before they can reach the fort. Use catapults here ... their anti-personnel AOE damage is significant.
Communicate. Call out enemy positions so that people can move into position. A small number of defenders can hold the fort against superior numbers if the move quickly to the right spots.
Against Tenacity
If the offense has tenacity, then you outnumber them. Use this to your advantage.
Send a large team south to the towers. The faster you switch the damage buff, the less impact all that tenacity will have on you.
Use your communications to move troops to the enemy assault point. You should always be able to zerg any enemy attack.
Get outside the fort. Their tanks have extra health and need to be attacked as soon as possible. Don't worry about dying ... with good numbers, a steady flow of rezzing players, picking up RPGs as they come down the hill, is a good thing.
Never let the enemy occupy a room in the fort. They will bring in tanks and use the guns to bomb the door. If a wall goes down, zerg that room immediately.