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They are mentioned in: United States Army in World War 2, The Technical Services, the Corps of Engineers, pages 93, 171, 242.
Starting in March 1943 the 345th Engineers General Service Regiment, with no previous experience in building pipelines, built a 160 mile gasoline pipeline from Casablanca, Morocco to Marrekech to supply the Army Transport Command & North African Training Command. At this time they were probably under command of the Atlantic Base Section.
By 10 Oct, the first full-sized convoy into Naples, Italy brought the 345th EGSR. They were attached to the Fifth Army Base Section, which on 28 Oct became the Peninsular Base Section. The unit was the first base section engineer construction organization in Naples. its early assignments included mine clearing, setting up an engineer & a quartermaster depot, repairing railroads, building POW camps, & working on the Serino aqueduct. The 345th was also responsible for all street & sewer repair in Naples, althought civilians did the actual work.
I think there is more mentions of their later work under PBS in the book: Corp of Engineers, The War Against Germany.