In mine, I have the Pioneer radio, but the solution should be the same. Get your Onyx with the car kit, and plug it into the auxiliary input in the front of the radio. I put the suction cup on the windshield for now to hold the radio, but I do plan on permanently mounting it later. You can get a mount specific for your chassis from
SiriusXM Satellite Radios, Antennas, Accessories and More | TSS-Radio
Let me know if you have further questions, I've done this in a couple of my trucks.
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