I believe I have found the portion that you are missing for the weapon mounts.
Unfortunately I am not familiar with C# at all, so I can't help code this. Perhaps my next programming course will be C#....
<weaponMounts>
<mount x="540" y="170" rotate="true" mirror="true" gib="6" slide="up"/>
<mount x="540" y="274" rotate="true" mirror="false" gib="6" slide="down"/>
<mount x="390" y="135" rotate="true" mirror="true" gib="5" slide="up"/>
<mount x="390" y="309" rotate="true" mirror="false" gib="5" slide="down"/>
<!-- artillery mounts testing -->
<mount x="540" y="170" rotate="true" mirror="true" gib="6" slide="up"/>
<mount x="540" y="274" rotate="true" mirror="false" gib="6" slide="down"/>
<mount x="390" y="135" rotate="true" mirror="true" gib="5" slide="up"/>
<mount x="390" y="309" rotate="true" mirror="false" gib="5" slide="down"/>
</weaponMounts>
<!-- Bad combos
1+3; 1+5; 1+6; 1+3+5; 1+3+6; 1+5+6; 1+3+5+6;
any combo of numbers with 6 if there is not 5
-->
<explosion>
<gib1>
<velocity min="0.6" max="1"/>
<direction min="60" max="120"/>
<angular min="-0.4" max="-0.1"/>
<x>8</x>
<y>127</y>
</gib2>
<gib2>
<velocity min="0" max="0.4"/>
<direction min="0" max="90"/>
<angular min="-0.4" max="0"/>
<x>38</x>
<y>36</y>
</gib2>
<gib3>
<velocity min="0.5" max="1"/>
<direction min="-40" max="90"/>
<angular min="-0.5" max="1"/>
<x>48</x>
<y>6</y>
</gib3>
<gib4>
<velocity min="0.4" max="1"/>
<direction min="120" max="200"/>
<angular min= "-0.2" max="1"/>
<x>51</x>
<y>206</y>
</gib4>
<gib5>
<velocity min="0" max="0.5"/>
<direction min="230" max="310"/>
<angular min= "-0.2" max="0.2"/>
<x>187</x>
<y>57</y>
</gib5>
<gib6>
<velocity min="0.6" max="1"/>
<direction min="240" max="300"/>
<angular min= "-1" max="1"/>
<x>388</x>
<y>120</y>
</gib6>
</explosion>
This is direct from the Kestrel.xml file. I haven't been able to identify the img file for the individual weapons for them to be utilized in the editor.
As a side note, I would suggest combining the options form into the ship design form if you are able. This would streamline the program's use, as well as allow the adjustment of weapon sprite placeholders.
I am currently working on figuring out if these lines are static or dynamic in relation to the weapons used. Since all of the weapons "jump" into the same positions on the ship, I would believe that these are static placements in regards to the base ship design and placement. If this is the case, then a simple "transparent placeholder" entitled "Weapons Mount 1" and so on would do the job nicely. All that the placeholder would need to do is designate where the weapon placeholder is in the X/Y grid that the game uses. Since the ShipEditor already does this with the base ship and its rooms, this should be a fairly easy patch.