I too have the removable tour pack added to an 08 Road King. I rarely took it off, except for a thorough cleaning, BUT when riding solo, the tour pack mounts rattle gong over bumps. Some people have used shrink tubing to pad the front grommets, I tried cable ties, to no great success. Since I added a radio antenna to the tour pack, I almost never take it off due to the added complexity of wire connections. If you have the "permanent" mount, it probably doesnt rattle and I'd stick with that if you ride solo vary much.
The "slide forward" to make a solo seat back rest is an interesting idea, but assocoated wiring would have to lengthened to accommodate that.