Bruce,
Which Cabelas screen room you looking into? I have thought about the Alaskan Guide Gazebo. It is advertized at 12x15. This is a bit misleading. The 15' dim. is between two corners of the hexagon footprint. Our 550 will fit. I invision using it w/o putting the TD inside, but could if the weather dictated. This screen room is pricey, but should be the last one we would need. It does come with the full coverage rainfly. I like your ideas about the poles for the side tent.
Steve