I'll add my thanks for your write up... just finished installing a three-camera BlackVue setup with the battery backup instead of the PMP, but it was still largely based on your advice and write up. MUCH appreciated!
The newer F-150 builds (presumably Job #2) can access the cargo, hitch, and backup cameras at speed. We posted some videos and info in this thread. It looked like I could probably access a trailer camera as well (at least the expensive Ford one) but I don't have that so cannot confirm.