I'm not sure what you want help with... Perhaps if you explained your vision a bit more about the picture?

What I see is
A truck, next to a building, near a park with a tree...

You mention Darth Vader, and lightsabers, but you want help with the truck. I'm not sure how to help with the truck because:

What world is this?
What building is that?
Where is this taking place?
Why is Darth Vader there?
What type of truck do you intend it to be?
What's with all the (not so)whitespace at the bottom?
You have a sepia palette. Will the entire picture be in that style? or just those objects?

I'm not sure I can help if you don't tell us what you're looking for...

On that note, the line work on the truck could be refined. Mostly the wheels and under-carriage, and possibly the logo on the side. But for the most part it fits in with the rest of your style.