The vehicle is cramped and uncomfortable for humans but the Karks like it that way, their traditional form of social interaction being to stand or swim in close proximity to each other. The vehicles carry four large boxes which are filled with water before the vehicle goes on a mission, as when the squad deploys the rear door opens and much of the water in the vehicle escapes. When the squad remounts, the door is closed and the water pours from the spare tanks into the vehicle. The Karks can get by indefinitely without water, as they can extract oxygen from air as well as water, but they greatly prefer to have water flowing over their gills.
Khurasan preview the Karkwagon
Khurasan Miniatures have posted photos and background details for their 15mm sci-fi Karkwagon vehicle. From their announcement: