Ola Philip
A diorama usually is a base with some figures and some kind of story. So if you want only the vehicle on a piece of groundwork I think that would be called a Display....... Well enough Lecture about Dio`s and Displays and such.
One of the easiest ways of doing this is:
Take a piece of wood/MDF/Pictureframe/etc./etc/
Make some leveling with some sort of Foam. ie. a roadbed with grass on both sides of it. Fairly easy to do.
When you have done that glue all the foam on to each other with white glue.
When that has dried put a layer of Wallspackle on it. Wallspackle = wallfilling compound. Really cheap and comes in a big tube. Can be found in the DIY stores.
When the Spackle is still wet sprinkle Birdcage sand over it. And right after you have done that press the vehicle a couple of times in it to get Tire or track prints.
Smear white glue on some patches ie. the roadsides and such. Sprinkle Static grass on it (can be found at railroadshops and modelshops).
Birdcage sand is white and not much in land sands are that white. So you can decide to paint it. Paint it in Sandy yellow or similar tones. Static grass the small fiber is really green (Hurting your eyes green) so you can decide to paint that too. When all is done you can put on your vehicle glue it to the base with white glueor leave it as is.
Last but not least you could do some dusting with Pigments or Pastels to tie the model in with the base.
Basically this is Display building in a nutshell. There are way more tricks then I can tell here. I suggest you trying the Diorama articles section of this site. Which can be found
Here Hope this is of some help for you and I would like to see the results when you have made something.... Pics are always welcome