ask yourself first...what do you want to add as scenery?
Desert, mud, snow, road, field, steppe, woods, stream, street, building, ditch, rail road, sidewalk, bank, hole, river, ridge, bridge, hedgerow, brush, crops, all can be replicated in miniature for your vignette or diorama.
There are several commercialy available products as well as those you can make yourself. Roots of woody plants make great trees when turned over and trimmed to size, cisal rope or cord makes great tall grass, static grass can be purchased for short grass, dried flowers are good for plants and there is a whole cottage industry built around scenic treatments. You can make trees from wire wound together and covered with milliput or aves apoxie, tissue paper with glue and water makes great tarps in addition to tree bark or husks for palm trees.
Resin for water, celuclay for earth, snow and rock, plaster, fimo, sculpey, real rocks, sand from the garden or the Home Depot, kitty litter makes nice gravel or smaller rocks, and there are a as many recipies for mud as there are applications of it.
What sort of scene are you looking to build, what are you showing, how large, how small, what is the feeling or message or "picture" you're trying to convey? Questions you need to think about when diving into a project like this.
Make several sketches and plan out what you want the scene to be. Are buildings included, figures, what theatre of operations is the vehicle in? What time of year? Before, after or during a battle?
You can make paper cut outs after the sketch stage and move them around on your base to get a feel for placement, scene continuity, scale etc. Once you think you have something then start on your building of the terrain, architecture if any, terrain features, placement, etc. Ask yourself, what materials you will need, are there drying times or set-up times to consider, what logical progression of steps will you need to do things in to take into consideration materials, chemistry if any, and ease of access for painting or detailing?
Are you looking for a full blown diorama or just a base to put some "environment" around your vehicle?
Once I think you narrow it down, I'm sure plenty of folks will be able to hop on board and give you a plethora of information, techniques, tips and tricks to accomplish your project. This is a great place to find loads of help.
Good luck.