Post your designs here!

I made the aimer railguns as accurate as possible without affecting the mass too much because I was under the impression that the AI for aiming fixed weapons tolerates a larger aiming error the wider your spread angle is, and this seems to be the case if you watch the tracers coming in. Even very large spreads on spinal weapons tend to just catch the target with the edge with most if not all of the projectiles falling to one side. At the 50km launch range which I eventually settled on this effect doesn't seem all that significant but a few cm of aerogel is so light and reducing it doesn't seem to affect the hull diameter at all so I didn't see any point in taking it off.
The rate of fire was just so I could use the tracers to get a rough idea of how close the drones would get before they started losing their firing solution, but the Apophys reactor with radiators is so light at ~450g in a 130kg weapon system that again there didn't seem to be any need to remove it, and against very lightly armored ships like the cutter or marauder the railguns can actually make a worthwhile contribution. I didn't think of the ship crew requirements though.
As you say the performance is not great for such a massive weapon. The drone bus could probably lose a few tons by going down to ~8km/s instead of 13 without losing too much punch (although the submunitions and flak bombs would all have to be recalibrated). The mass to payload ratio in the bazooka drones is not too bad, better than a stock flak missile with twice the launch velocity, although there is a lot of waste from bomblets which don't hit the target. You might be able to get an even better ratio by making the clusterbomb into an unguided rocket, potentially allowing many kilograms of octogen to be removed from the blast launchers, but the burn time would have to be very short in order to not throw off the aim too much.

Edit: effect on target seems to be improved by increasing the hard range on the 36g pieces flak bomblets, however this does increase the risk of flak being detonated prematurely (either by ship geometry not matching the proximity sphere or flares launched towards the flak) and being deleted before it can do anything. I was quite conservative with 100m but 150-180 seems like a good balance.

That's 2866 times the mass of my MLRS/torp skiff...

I got a bit annoyed by the nasty lady in Vesta Overkill, so I developed this ship and corresponding needle gun drone to get my revenge. The lasers act as drone killers in order to not send the game into crawl mode with the needle payloads from the main guns. Turned out the extended delta-v comes in mighty handy in Dusk over Triton.

Ok, so where do I find the export folder on a linux machine?

CraftBlueprint AACTestboat
Modules
1.01 GW Thermoelectric Fission Reactor 1 0 null 0 0
6.44 km/s Methane Gimballed Nuclear Thermal Rocket 5 0 null 0 0
6x3 Aluminum Radiator 2 92.648 30 Crew Module 2 0 0
35 Crew Module 2 1 0.97207 null 0 0
30 Crew Module 2 1 0.037073 null 0 0
30x8 Boron Nitride Radiator 2 74.3 1.01 GW Thermoelectric Fission Reactor 0 0
690 t Methane Tank 1 0.48604 null 0 0
800 t Methane Tank 3 0 null 0 0
666 MW Nd:YAG Near Ultraviolet Laser 1 10.798 null 0 1
50x7 Amorphous Carbon Radiator 2 17.846 666 MW Nd:YAG Near Ultraviolet Laser 0 0
11.0 m x 1.80 m Spacer 1 25.982 null 0 0
Zwecke V6 3 144.65 null 0 0
Zwecke V6 5 105.94 null 0.25 0
30x8 Boron Nitride Radiator 2 56.313 1.01 GW Thermoelectric Fission Reactor 0 0
666 MW Nd:YAG Near Ultraviolet Laser Turret Mount 4 87.297 null 0.78 0
50.0 MW Zecke Launcher 2 73.657 null 1.56 0
5x2 Silicon Nitride Radiator 2 89.749 50.0 MW Zecke Launcher 0 0
12x Zecke 1 1.2295 null 0 0
6x2 Silicon Dioxide Radiator 2 95.253 35 Crew Module 2 0 0
50x7 Amorphous Carbon Radiator 2 38.086 666 MW Nd:YAG Near Ultraviolet Laser 0 0
5.40 m x 2.40 m Spacer 1 0.62463 null 0 0
Zwecke V6 1 165.31 null 0 0
14.6 m Diameter Lithium-6 Radiation Shield 1 0 null 0 0
70.0 km/s 986 MW Methane Gimballed Magnetoplasmadynamic Thruster 1 0 null 0 0
Armor
Shape Cylindrical
Concave true
ArmorLayers
Aramid Fiber 0.001 0 0 1 1 0
Boron Filament 0.01 0 0 1 1 0
Amorphous Carbon 0.048 0.05 0 1 1 0
Graphite Aerogel 0.5 0.05 0 1 1 0
Tin 0.001 0.2 0 1 1 0
Graphite Aerogel 0.5 0.05 0 1 1 0
Osmium 0.0005 0.02 0 1 1 0

Do note that said export should include all sub-entities, e.g. all Zeckes and all Zweckes too, and any custom stuff. You can also prefix it all (rename entities) with some tag.