Propagation tends to be across the ground plane. Other than that, there isn't much to consider. In general the outer shielded part of the coax and radio are generally electrically connected to the entire metal part of the vehicle body. An unconnected piece of metal near the antenna may affect it in a minor way, but not likely to be measurable or significantly measurable.
It will be generally more practical to make sure the tent rack has strong electrical continuity to the body of the Jeep and each section likewise carries continuity to where the antenna is mounted.
Don't over think this, it's easy and simple.