The Roamer

Dunno, but the Roamer (according to the DVD commentary) was built on a Volkswagen Thing chassis, not a Beetle or a Volkswagen van as stated in the trivia and commnts here.

As a side note to the side note, in the series Bible (available on the DVD extras) the Ark was just the Ark and the Roamer was originally a domed Jeep-like vehicle called the Ark 2:

"As the Ark is somewhat cumbersome and cannot always maneuver itself through certain terrains, ARK TWO is brought into play, Ark Two being a plastic airtight domed jeep that is used for foraging when anyone or number of the team must leave Home Base. The Ark Two carries oxygen and limited supplies, the Home Base being the storage house for most of their needs. Both vehicles run on hydro-power, a system that converts water into hydrogen as its main source of power. The same system services the heating and air-conditioning of the Home Base, also providing light and power for their electrical equipment."

Throughout the 80s people travelling on I94 east of Kenosha Wisconsin could see the Roamer. It was parked on a concrete pedestal in the parking lot of some small company, a garage or charter bus company I think.
Unfortunately when I went back to take photos of it in 2000, the Roamer was gone. No idea where it is now.