Centering on the flatbed is a pain and I have to use a spotter who matches up center lines on the camper and bed, but we are getting better this each time. Loading my AF into a pickup bed was pretty simple since I could just watch the tailgate opening as I backed up.
Right now I'm pretty happy with my spotter (DW) and don't think I need to replace her with guides. Twice I have loaded my TC without help, but it took multiple trips in and out of the cab to make sure I was still centered since I cannot see the reference lines.