Are these restricted to PDC's? Or could you add them to a hull to created a mobile support base?
You can put them on a ship but the ship needs to be in orbit of a population (even just an asteroid temporarily designated as a colony) for the modules to have an effect. It makes life considerably easier when everything is handled at the colony level. If you have several ships (or PDCs), all their modules are added together and added to the total of any maintenance facilities on the planet. So if you had a fleet of maintenance ships with say 5 modules each, if you assemble ten of them together you can maintain and overhaul 10,000 ton ships. PDCs are probably going to be easier though because you can prefab them fairly quickly and assemble them where you need a base.
The ship-based maintenance modules, along with some support ships to transport minerals, fuel and maintenance supplies, could be used as a temporary forward base for survey ships
Steve