Same question - I have a jump seat and want to install USB chargers and 12V outlet in the rear..
any info on wiring harness that can accommodate, would be super handy.
I saw some online on a web site that sells them. pretty nice lookin, actually.
https://www.roughcountry.com/rc-gm-pocket-fender-flares-f-c12011.html?find=2020-chevy-silverado-2500-hd-4wd-740497
[Not my truck.. pic from customer reviews on the product page above]