Ahhh I see, sorry for the confusion.
My first thought was if you would replace the heavy onslaught cannon with another laser destroyer to make it double barrelled, you'd get a grav version of the apocalypse tank from red alert 2.
Courtesy of Gael Knight over on dakkadakka. It looks a million times better
Agreed, it looks more like an actual battle tank rather than this weird transport/gun boat thing they've got going on at the moment.
Two onslaught gatling cannons would have been amazing too, maximum dakka!