Tie them both to the frame of the AS at one point. The one to the copper was to ground the plumbing for lightning protection as well. PEX doesn't have the same issue electrically as copper. Mine is grounded just forward of the rear bumper to a big bolted in brass lug. There are two ground wires in the lug.
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'The Silver HamShack' (2007 International 22FB CCD 75th Aniversary model)
Multiple Yaesu Radios inside and many antennae sprouting from roof, ProPride hitch
2012 shortbed crewcab 4x4 Toyota Taco TV with more antennae on it