Take a look at this classic Verlinden diorama;
It contains the same basic elements that you are using; a tank, a building, a car, a road intersection and some figures. No matter what you do, the building has to go in back, otherwise it blocks your normal viewing perspective. Play around with this basic configuration, reversing the positions of the tank and jeep and their orientations. Try to think of something that they could be doing; fixing the tank, the jeep, a roadblock, a check-point, refueling/rearming, or whatever you want.
Just remember not to line-up objects in the diorama, (the roads, building sides, tank, etc.), parallel to the edges of the border, keep everything on the diagonal, dioramas alined with the border don't look right.
Good luck! 