The trunk will be sold, and seems the black born part beauties win out again for a good price. I have heard of folks putting the antenna in the fairing...provided it doesn’t play bad with the Rosta, we should be good to go.
I did this with my Supervalked '01 I/S. Used an amplified Dakota Digital unit - AM-FM reception only.
At present there's a set of modified I/S rails on the bike. The studs were cut off and ground flush then drilled and tapped. M8 flange nuts were welded to the inside of the two rear mount tabs prior to tapping those holes, and after smoothing things down the rails were powdercoated gloss black. I also converted another set of the I/S rails and had them re-chromed. Should I want to run a trunk with one or both antennas (the other being for the CB and a ham radio transceiver) it's a simple matter of four bolts and some wire connections. Would probably take me less time to install the trunk than it did to type this paragraph.
Another rail option: Get a set of Std/Tourer rails with the sissybar side plates and sissybar. Scrounge around for a Hondaline CB antenna mount plate that fits the sissybar setup, and install the mount along with the antenna. If you have a CB, put it in the battery box behind the battery. You'll have to trim part of the box to allow it to fit; when I did installations of this sort I placed two wedges made from closed-cell foam in the cutout area with the transceiver body. The wedges act as packing/cushioning. Last thing you'll need is the AM-FM/CB "splitter" from a GL1100A; eBay usually has several listed and Sierra Electronics carries them new. This allows you to use the CB antenna as the AM-FM reception antenna.