The build information link is on every page of 4x4labs web site.
It says "rear bumper build instructions". When you click on it you can see the pics Woody just posted.
I'm sure you are aware of that right?
It looks like the parts are all there. Look at the tire kit parts and separate them, do the same for the can kit. What's left? The main bumper which looks pretty basic. Might just be a case of poopy pants.