For the ground, the proper way is to have less than 1 ohm of resistance back to the battery. On the rear wall (Factory Ground Point), you will see from 0.5 to 10ohms. Why is that? Well, these trucks are glued together, and depending on the age of your truck, the incline it's on or if it's moving down the road, it will change.
If you want to ensure it's done right, go to the battery for the ground. If you enjoy inconsistencies and hours of your life wasted on troubleshooting, you can try the rear wall. The cheaper the gear, the less susceptible it is to a bad ground. Good equipment, it will hate life with the factory ground point.
Here is a video that helps show you a low-invasive, safe way to run the power/ground cables