Personally, I think that it should be built-in to every ship that can launch them, and it should match up with their description. IE, the big ships can store the two-ship bay, gunship and keelback are limited to the single-ship bay. Ships like the Cutter, Conda, and Vette are not hurt by the SLFs requiring their own slot, as they have enough slots in them that any pilot who wants to fit the module can shuffle his stuff around without too much trouble. The Gunship and Keelback suffer greatly, and they don't need the extra suffering imo.
However, I am also an advocate of creating "slots" in the sensors module, so that higher grade sensors can "slot in" stuff like the advanced disco scanner and DSS, but that's another topic.