Thanks for all the tips! I have marker lights that run off the pigtail that I can plug into my 7-way receptacle - I was planning on making another pigtail with a flat 4-way plug for the new taillights (my Ram has 2 receptacles at the rear bumper)
I was concerned that the camper obscures my 3rd brakelight; and with only one taillight being visible at times, I might attract the wrong kind of police attention?
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Re the tailgate: yes, I was told to use the tailgate to support the back of the camper. But I appreciate the mention of debris hitting the underside of the tailgate.... I still have some extra transit shield laying around somewhere - I'll just cover it with that.