'Buildings' would be easy to make (as easy as ships, anyways). Even turret buildings that had a helm and could be rotated on a base.
Step 1. Make the building.
Step 2. Make the building a ship with a noclip base (no collision on the lower part so you can sink it into things)
Step 3. Give the ship a billion mass, lateral drag, and vertical drag (this is so it can't be moved).
Step 4. Give it a 'gear room' with engines that can turn the ship, and give them enough power to turn the massive mass.
Step 5. Make a static base model to place in the map.
Step 6. Spawn ship/building/turret over static base.
Step 7. Win.
If you choose not to spawn as a 'turret', the spawn would still apply, but your ship would spawn over the platform as well, and you fly away.