I am sorry that I cannot provide the details for your specific truck. We need some stickies and a collection of data for different trucks. I can give you a brief explanation of what I did for my 2010 Ram 2500 and my 2018 Ram 3500.
For both trucks there was no feasible way to access the rear of the radio/nav systems. For both trucks the wiring for the Sirius radio had connectors. For the 2010, there was a connector just above the floor and in front of the door on the passenger side. For the 2018, the connector was located on the passenger side behind the grab handle on the pillar. For the 2010 I found an inexpensive magnetic mount puck that I placed on the hood on the passenger side. Snaking the wiring so it was inconspicuous took an hour or so. For the 2018, I could not find a suitable antenna online. I paid Dodge about $100 for a new shark fin style antenna and wiring. I glued rare earth HD magnets to the base so it would stick on the hood, again on the passenger side.
No matter where you place the antenna, you will sometimes lose the signal due to mountains, trees or other obstructions. With the hood mount position the camper will also sometimes block the signal, but in open areas it works well over 90% of the time. That is enough not to bother trying to mount the antenna on the roof of the camper.