Generally, this is what I find a lot of sportsmobile to look like.
The make a grounding pad, usually at the wheel well, they also attach a bus for a few items that are directly attached back to the ground pad. Many of the circuits are attached to the body/frame. Hopefully you have just one ground wire going to the battery. The manual says to attach close to the battery, but you need to keep it inside. You instead put the shunt inside between the battery and grounding location. If you are good, you might get away with just cutting the cable and splicing in the terminals to make the attachment. if you do have to add wire, it should be same size as the existing ground cable. It should not have to be that long.
Remember, for the shunt to be accurate all current that is read needs to go through the shunt, so there can't be any other connections to the battery pass the shunt.
I hope this adds more clarity