https://www.pcgamer.com/fortnite-port-a-forts/

A new item that could shake up how building battles play out in Fortnite is now being teased at in the New Updates bulletin that pops up anytime you launch the Battle Royale mode. 

Dubbed Port-a-Forts, the items sprout "a quick defensive position upon impact." It's unclear what type of fort they'll spawn, though I'd wager they make the basic recon fort or variations of it. We're assuming it's a throwable and not a trap-based item due to the use of "impact" in its description.