For what you want to do, the trailer harness/module would not be a good solution. The trailer harness output does not have wires that can be tapped...only the integral 9-pin connector. You would have to plug in a mating connector and then wire from there. If you actually installed the module in the saddlebag, that would have to be an external connection. The 9-pin connector would be an additiuonal cost. It would be better to purchase an aftermarket, isolated (powered) trailer module, and wire your additional lights from the output wires on that. It would not be plug-n-play.
Another, possibly better, alternative would be to purchase some of the great aftermarket lights specifically designed and marketed for the RT. The ESI HMT Brakelight, BrightSides, and their Mudflap Lights are great examples. There are also LED strips from TricLED and KewlMetal. All of these are site sponsors, and can be found on the SpyderLovers home page. Many of their products are plug-n-play, and come with great instructions.