First time I've seen a CT narrower than 205 in a 17" diameter. eBay has them for cheaper, $53.57, which makes it more interesting to experiment with.
I'm Darksider #1 on the FJR forum, btw.
Still, I just got nearly 18k from a Mitas EO7 Dakar, so not really worried about tire life at the moment. Get one and find a auto tire shop to mount it on your "side car wheel". They won't be able to balance it, but the moto shop can, if you want to do the two trips thing, (and are not doing it yourself).
You may need to fabricate a brake caliper tension bar out of flat stock to avoid rubbing at the sidewall. No big deal, just remember to radius the ends so you have free movement when the swingarm moves up and down. Other than that, use the same hole spacing as the original. I prefer 3/16" thickness bar stock. Stainless is nice, but paint on mild steel is easier.
There are some people on the Darkside forum running them on BMWs and Harleys so far. I don't play there, but it might be worth signing up if you wanted to ping them. On the face of it, it meets my basic criteria for a DS tire. A little square in the shoulder perhaps, but I wonder why it's available here. I see only the Opel Speedster as listed fitment.