From the Huge Ship rules (which can be found on FFG product page)
Huge ships follow all standard setup rules. However, during setup, a huge
ship’s bases may extend outside of Range 1 (or a mission’s specified setup
area) as long as the ship fully occupies the length of that area.
A huge ship cannot be placed with any portion of its bases outside the play
area. A huge ship’s figure may extend outside the play area at any time as
long as the base remains in the play area.
Edit: to summarise - the same way as all other ships; they're just bigger.