I've personally tried making some stuff in blender. A few weeks ago, I successfully made a truck that looks like the standard DAF Semi from this game. (Blender model only, no submesh)
Making stuff in Blender isn't as easy as most people think, But at the same time, Isn't ridiculously tough.
My advice is to try making some simple car models in Blender, Search for online guides for "low-poly vehicles".
Once you get some practice, Follow the Documentation and design a submesh and write truckfiles for your vehicle.