SB's dont hardly appear in the yards. So they are usually placed at the outset of the campaign, or added during.
Tell me about it! In five years of playing I have never seen a Gorn SB in the yards.
However, with Bonk's way-cool shipyard protocals, will this be an issue at all for you?
I'll tell you my dream base construction scenario.
BaseStation: Mission is offered in every friendly hex. Places a base if you win, you lose the base if you lose.
BattleStation: Mission is offered only in hexes where a BaseStation already exists. If successful, replaces the base with a battle if you win, you lose the battlestation if you lose but the base remains.
Starbases: Mission is offered only in hexes where a BattleStation already exists. If succesful, replaces the battle with a starbase. If you lose then the battlestation remains but you lose the starbase.
All bases would be hidiously expensive, but unlike starships would always be available for purchase if you have the scratch.
-S'Cipio