A Guide to Freighter Outfitting
The first thing you need to understand is that all the freighters have far more hardpoint capacity than powerplant capacity. To shoot down enemies quickly, the premise you must place above all is energy efficiency . The most energy-efficient way to kill a ship is to remove its shields with shield-buster guns, then kill it with missiles. You can load up a freighter with 8 regular guns, and kill a ship or two with it - and then you'll be shooting two guns while your depleted powerplant struggles to squeeze out a trickle of energy.
If you're loading a freighter for combat against shielded enemy ships, one must always start with the shieldbusters. There aren't a whole lot of shield-buster guns in the game, so you want to start your choices with this. One isn't enough; you want two in a matched pair, and you want to use shieldbuster turrets if possible to keep the gun slots available for missiles.
Freighters of class-4 and below should use Adv.Stunpulse guns or Stunpulse turrets. A class-5 Crusader can use either those or Corsair Borroco guns. Class-6 freighters should use two Debilitator turrets, and the Humpback can use either those or the class-7 Debilitator gun or Corsair Rapier.
Next, load your ship with missile launchers. Don't bother with the stalker-type missiles; they don't do enough damage. Get a Slingshot for class-4 and under, a Catapult for class 5 and 6, and the Humpback can use either a Lancer or cash-efficient Catapult. I recommend taking two missile launchers. If you expect short fights and don't mind spending extra cash (generally true during the SP campaign), take two of the highest class; if you think you might run out of ammo or want to be cheaper, take one of the next class lower.
You should have about four hardpoints left now. This is fine, because the freighter ships' powerplants are only really capable of sustaining three or four guns of the ship's maximum weapons class. These guns will be determined by two criteria: matching the projectile speeds to your shieldbusters, and energy efficiency (damage per energy used.) Matching the projectile speed is critical because if you don't, the crosshair won't be accurate and your shots won't hit. Matching the range and refire rates aren't necessary.
So, following these rules, let's outfit a Dromedary. We start with two class-6 Debilitator turrets (make sure to put them in slots that can fire forward), and add two class-5 Catapult missiles. This leaves us one class-6 gun slot, two class-5 turret slots, and one class-6 turret slot. The Debilitators are 700 m/s projectile velocity, so everything else should match that. The most energy-efficient class-6 700 m/s gun is the LWB Adv.Devastator. The most energy-efficient class-5 700 m/s turret is the Corsair Angelito Mk I, and the appropriate class-6 turret is the GMG Sunblast.
Of course, if you don't want to go mucking around with the LWB during the campaign, you can use easier-to-get equipment like an Outcast Dragoon gun instead.
There you go - a perfect Dromedary. Of course, you need to get the hang of its fighting style as well. Fly at a target ship head-on, your shieldbusters will take off the shields, you'll launch a pair of Catapults, and clean up as necessary with the rest of the guns. With practice, you should be able to take out AI ships of up to class-8 (basically anything you'll meet in the campaign) in one head-on pass. Then fire the thruster, kill the engine, drift out of danger while turning around and lining up another target and replenishing the powerplant, and repeat.
Also, the rules change in the SP campaign for the missions where you'll be shooting at only unshielded targets, which is all of mission 12 and 13. The only rule here is energy efficiency, energy efficiency, energy efficiency. Of course, you should keep the two missiles, and add mines for whacking large stationary targets. Other than that, you just want the most energy-efficient turrets available. (The Order Reaper turret is excellent, although you have to either acquire 650 m/s guns ahead of time or live with a speed mismatch between your guns and the turret.)
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