I like these as well but with 4 gals in the group I really need a "wet" water supplied toilet... after looking at all the options that australian companies have to offer seems like in the U.S. we're lacking options for "larger" offraod campers like
http://www.kimberleykaravans.com/off-road-caravans
http://spinifexcaravans.com.au/caravan-models/
http://www.marketdirect.com.au/