When the rebs here claimed it was a Customs House I started doing some surfing. It turns out Sumter was not even completed even though it was under construction for over 30 years. It sounds like it was a Federal Boondoggle project and was never actually 'open for business' let alone as a customs house.
A preliminary survey of the entire coastline of the fledgling United States was begun in 1817, and by 1828 plans had been drawn and adopted for Ft. Sumter¹s construction. In the introspective atmosphere of the Ante-Bellum United States, which expected little chance of naval assault from any foreign nation, construction on the new fort was slow and in 1834, with only its granite foundation above the water¹s surface, construction was halted altogether due to an ownership dispute over the actual property on which the fort sat. Construction resumed in January of 1841but by 1860, on the eve of South Carolina¹s secession from the Union, the fort was still incomplete.When South Carolina seceded on December 20, 1860 Ft. Sumter¹s outward appearance was impressive towering nearly 60 feet above the water¹s surface, with masonry walls five feet thick, and three levels of guns on four of its five sides, but the barracks and the officer¹s quarters, which lined the fort¹s rear 317 foot gorge wall were still under construction. If one took the time to inspect the structure further they would also have noticed that many of the second tier gun embrasures remained opened, each about 15 feet square. Much work still remained to be done. Despite its incomplete state, Sumter was the most recently armed of all the United States forts with potential to mount 135 guns, however, only 10 of these weapons were actually mounted, all defiantly facing the Atlantic Ocean. The balance of the fort¹s weapons were stacked on the parade ground. Along with piles of construction sand and a city of storage sheds.
One mile to the north-east, across the entrance of Charleston Harbor on the southern tip of Sullivan¹s Island, sat Ft. Moultrie and its 80-odd man garrison of the First United States Artillery. Moultrie was the polar opposite of Sumter; it was as old as the hills and was barely 11 feet in height with delapidated walls upon which decades of sand drift had accumulated. It was no uncommon sight to find local cows grazing on the weeds that grew out of Moultrie¹s ancient masonry walls. As secession became a reality, Moultrie¹s meagher garrison was the only organized force available to resist the state¹s action. Hopelessly outnumbered by hostile civilians and state militia, Moultrie¹s commander, Kentuckian Major Robert Anderson, decided to transfer his tiny garrison across the channel to the much more defensible Ft. Sumter. At Sumter Anderson could be re-supplied and reinforced more easily than at Moultrie, and if his government desired, he would be in a position to bottle up Charleston Harbor to all outside shipping. In a text book maneuver during the night of December 26-27, 1860 Anderson and his men slipped across the water and occupied Ft. Sumter. When the citizenry of Charleston awoke the morning of the 27th to find U.S. forces occupying the strongest bastion in the new Palmetto Republic, all hell broke loose!
Source: http://www.civilwarcharleston.com/fort_sumter.html
Nothing suggests Sumter was ever a customs house. Just more fables from the modern day appogilists for the Southern Slavocarcy.