First a caution. Grimshine's Berzerker has its overload damage set at 16,500. For some reason (probably oversight), the standard Berzerker had its overload damage left at 1200. That is the primary reason the Berzerker can be made ultra-powerful, but even if it is nerfed to 16,500 this will still be very effective.
The ORIGINAL idea of the berzerker was that it gave an insanely generous firepower and defense buff for 12 seconds to all the other ships in the fleet regardless of distance (this buff has no Aura range), but you sacrificed a large portion of your ship health for the benefit, which Kixeye hoped you would repeat after coining the repair on the Berzerker(s). 1200 armor was a 20 minute repair back then! The Berzerker can now be given over 700,000 base armor for over 583 overloads. Since the hull has only 1hr repair time, about 48 overloads can be used and still have the Berzerker repair instantly. Even if Kixeye DOES nerf this and give it the same overload damage as the Grimshine's Berzerker, this still gives you 5 overloads for instant repair.
So what happens when the overload is triggered? When it is first triggered, everybody in the fleet immediately gets their reloads reset and fires their weapons. Then for the next 12 seconds, the reload for weapons on all ships is boosted by 3x. All ships get 30% speed and 20% turn speed boost. Ships affected by Coldsnap are released and immune to it. 1260 is added to the Survival for all types except Corrosive, that didn't exist when this ship was released. This defense boost also affects the Berzerker itself, giving it the added benefit of reducing damage to get the most from the overload period.
Since the Berzerker multiplies the power of all ships in the fleet by 3, it makes more sense to outfit the Berzerker to just take as much advantage of this as we can and waste no weight on weapons, and the other 4 ships in the fleet can provide the offense. This is best utilized with remote fire mortar and missile ships, but as long as the Berzerker is hanging out in front by a bit and feeding on damage, other types of ships can work along with it as well.
To build a Berzerker to do this, you need to add as many armor points as possible, and not worry about weight. 5 pieces of either type of Ferrite armor will do. This gives you about 700,000 base Armor. 1200 damage comes pretty fast, so adding an armor special will extend the time between overloads so you can get closer to a full 12 seconds. Add an Engine special, then just put on a Peacemaker I mortar to set range so the ship will move when on auto. That's it. You just have a brick with 700,000 Armor that gets shot at. However, when this is sighting for remote fire ships the carnage becomes unbelievable. The ships in back can even be zombies if they are far enough away from the action to avoid fire.
When and if the overload is nerfed to 16,500 you will probably want to ditch the armor special to keep the overload on. This will depend on how much damage your target type is dishing out.
Where do you get it? It is up there in your Foundry under the Garrison tab, and you probably already have it.