Jess, here's why a pillion doesn't work, it leaves too much open space around it. The trike body is shaped to fit the back half of the one piece OEM I/S seat which is much wider than the corider OEM pillion as used on the Tourer and Standard models.

Here's the pillion with my Ultimate King Boy. The pillion is in position, however the rider's seat is at least 2" forward of being able to latch in place. Plus I don't even have my backrest mounted at this point. I might call Ultimate to see what just the back seat of a 2-piece I/S set might cost.

The way the Roadsmith kit is mounted, the back half of the rear fender is removed. Granted, I could still use my rear fender bib which was designed to match the seat and tank bib. But as with the pillion, it leaves a gaping hole in back. I have a nice studded I/S seat that I would gladly trade for a stock ungarnished I/S seat if someone is interested. I hate the thought of cutting up this one.