Just put it ona  road with some trees and problem solved, you are in the all open section  ;D

The diorama rule has changed my angle of attack but ill still be entering, maybe in 2 categories.

From what iv'e read (correct me if im wrong) if the base is part of the kit out of the box, its ok.

e.g.

As soon as you add to that (flocking, plants, lighting) it becomes a diorama.