The rear-door antenna location would give you much better antenna "propagation" when talking to vehicles located ahead of you (on-coming traffic or convoy leader). However, I wonder if the rear-door antenna location would get snagged on a person's arm when loading cargo or hinder rear cargo door access. Further, you'd have to run the antenna cable all the way back up front to the CB (while trying to hide the cable under carpeting or body panels). The rear-door antenna location may be more headache than it's worth.