So, the Norse had cargo ships, but they weren't really "longships" in the sense that they were called different things by the Norse. I wrote about this here: https://www.reddit.com/r/AskHistorians/comments/33qpi1/why_didnt_or_did_they_viking_ships_have_roofs_or/

the tl;dr of that thread is the the Norse cargo ship, the knarr, seems to maybe have had a half-deck, but we can't be sure because literally only one remains, and it's in partial condition (the Skuldelev 1 wreck). Hope that helps -- please don't hesitate to post follow ups here, as that older thread is locked.