I don't think marker lights do much, but they certainly don't hurt. FWC is probably required to put them on the larger campers. My Fleet didn't have them. It is wider than the truck (Tacoma), so I put some reflective tape on the jack brackets, the widest point.
I did add a high stop light, which I think is important. It's just a strip of LED's above the door. Pretty easy to install but the wiring is something of a big deal because you have to tie into the truck wiring and install a connector. If you are going to do all that, for either circuit, you might as well do both. A 3-pin (or 4-pin) connector is no harder than a 2-pin. With this philosophy in mind, I also brought out the backup light circuit and connected it to the rear floodlight on the camper, through a switch.
I haven't gotten around to the marker lights yet.
- Bernard