The Gemara Shabbos 8a says that Abaye holds that one isn't liable for throwing a basket 6 tefachim (to circumscribe a 4x4 tefachim square) by 10 tefachim. Rashi explains that the vessel is its own domain, and only objects were thrown in the mishkan, not domains.
The Gemara (Eiruvin 90a) says that there is an argument between Rav and Shmuel whether one may carry on a ship relying on the walls of the ship. Rav says one can and Shmuel says one cannot.
The Halacha follows Rav.
Rashi and Tosfos both say that this argument is only regarding whether one says that the walls of a ship are considered "Asui Ledira" (made for dwelling) and if the ship is larger than a "Beis Saasaim", in which case the ship wouldn't be a Karfef shelo hukaf ledira annd one would be allowed to carry inside.
However, if the ship would be smaller, even Rav would agree that one can carry inside, as the Gemara says elsewhere Eiruvin 42 that a ship is considered to be like four cubits when it comes to Techum.
The Rambam Shabbos 14:2 writes that any object, whether it be a ship or a basket, as long as it's 4x4x10 it's a full private domain.
The Shulchan Aruch agrees.
For Shabbos, a keli can make its own Reshus.