First you should look at the Rhineland gunboat post.
http://www.lancersreactor.com/t/forum/t ... er&M=False

Which adds a pilotable Rhineland gunship with custom weapons/power.

and the one about the breton gunboat at
http://www.lancersreactor.com/t/forum/t ... er&M=False

Which tells you almost everything you need to do to add the Breton gunboat in.

In fact, all that really needs to be changed from that post is
from this:
hp_type = hp_gun_special_2, HpWeapon01
hp_type = hp_gun_special_2, HpWeapon02
hp_type = hp_turret_special_7, HpTurret_R3_01
hp_type = hp_turret_special_8, HpTurret_R4_01
hp_type = hp_turret_special_8, HpTurret_R4_02
hp_type = hp_turret_special_9, HpTurret_R4_03
hp_type = hp_turret_special_9, HpTurret_R4_04

to this:
hp_type=br_gunboat_turret01, HpTurret_B3_01
hp_type=br_gunboat_forward_gun01, HpTurret_B3_02
hp_type=br_gunboat_forward_gun01, HpTurret_B3_03
hp_type=br_gunboat_turret02, HpTurret_B4_01
hp_type=br_gunboat_turret02, HpTurret_B4_02
hp_type=br_gunboat_turret02, HpTurret_B4_03

You should get the UTF editor so you can look inside the .cmp files and see what hardpoints any ship has. You can also edit things like turret rotation angles.

NOTE: The Breton gunship is pretty limited without editing, since the Two Huge side guns, The top turret and the two belly turrets only shoot straight ahead, only the rear turret has 360 degree motion.
It also has no afterburner, and by default only has 3600 armor.

It's a big, heavy, clumsy sitting duck unless you edit the turrets so more than one can shoot backwards.
You'd also need to add some pretty powerfull guns, since you won't be able to run away, ever.

It doesn't look big, but if that thing would actually rest on the ground, a rhino freighter could fly underneath it.
It's wings come down on either side of the landing pads on Pittsburgh.

Cruising speed through asteroids, is, uh, not fun, since the autopilot can't handle it You can see the autopilot in action in Tau-31, and watch NPC gunships bash themselves to death on the iceteroids.

You have to edit the INI, namely Market_ships.ini among other things.

Try reading the thread "Compilations of IDS's .....explination of INI's"

It's a sticky near the top.