I’m installing a back up camera and want to know the best route to run wire from the rear cargo bin area to the head unit. Running under the door threshold does not seem that great (no other wires run this way). I can run along the side panels ( up and over the doors) and down the A pillar. I guess also I could go through the headliner. Anyone know the easiest route?

 

Just because they didn't run wires that way doesn't mean it's a bad idea. Most modern cars run whole sheaves of wires under the door treadplates precisely because it's easy, and it's my go-to routing method for backup cameras.

 

i ran my cb antenna cable from the rear door through the grommets and rubber tubing into the space at the base of the right rear corner of the truck, then up and behind the headliner. it's pretty simple to pry out the edge of the headliner above the doors and windows etc. -- usually without needing to remove too many pieces -- then tuck in the wire and push the headliner back into place. run it down behind the a-pillar and there you have it at the dashboard.
i'm not sure how easy it would be to get in behind the panels lower down in order to run under the door treads.

 

Try to follow the taillight or towing wiring.

 

How about running it out the firewall through one of the openings, under the truck along the frame rail and then up into the space behind the right side tail light and through the rubber boot with the other wires running to the door? I don't think there's any reason the cable needs to run inside the truck.