Wandered around here: Exterior Trim - Roof for 2018 Toyota Prius C | Toyota Parts Went to #13: Roof Molding - Toyota (75552-52190) | Toyota Parts Then down the page there's some items under "Customers Also Bought", not sure if anything's promising. Maybe "drip molding clip"?? Seems like there's several iterations of that rail?
I guess I could never figure out why you couldn't replace those bolts with studs, then slip the rack footing around the stud, then clamp the works with a nut on top. Never had a need for a roof rack on ours so I never gave it serious study but somehow it doesn't look that hard.
I briefly looked for rack options for our ‘12. I don’t really need it because we have a larger car we use for trips to carry us and stuff, and it has bars for a roof box. Still I figured if bases/towers weren’t that much I could swap the bars between cars.... no dice. I really liked the idea of putting our huge roof box (7.5’ x 3’ x 18”) on top of the C, even if it were just for taking a picture.
There are two possible solutions I've discovered doing a lot of research over the past 24 hours: 1) a custom track system installed on the roof to support crossbars, or 2) fabric covered foam "bars" installed with straps that go through the interior of your roof from one side to the other, a system known as a soft rack. I'm attaching a screenshot from a company called Rack Attack with an image and a list of parts for a system actually installed on a Prius C with the plastic roof rails. Rack Attack will install custom tracks along with crossbars, etc. for you at one of their locations, although I imagine there are other companies involved in this sort of business too, too. You can also find tracks from other companies by Googling "roof rack tracks" or "crossbar tracks." I was quoted $800 to 1100 for the full system installed depending on what specific products I choose to use. You could do it yourself if you're comfortable drilling through your car's roof. I most likely will either drive 6 hours to Atlanta or Tampa to visit a Rack Attack location or potentially get a trusted local body shop to install the tracks if they're willing to do that work. The fabric covered foam type known as soft racks are significantly less expensive. You can find a whole lot of different ones simply by Googling "soft racks." If I end up purchasing the used 2018 Prius C I'm looking at, I'll probably go with a real metal rack with custom tracks because I use my kayak for work, so my car with the rack on it gets parked for hours, usually sitting out in the sun because there's no shade available, while I'm paddling to one of my field sites and doing my shorebird surveys there. I question how long a soft rack would last would last with all that UV exposure. It certainly would not be as long-term a solution to carrying my kayak on a Prius C, and it might be worth it for me to pay for the more expensive system. But if you're involved in more occasional recreational use of a kayak or stand-up paddle board, the significantly cheaper soft rack solution might be better for you. I'm writing this more than 4 years after the post to which I'm replying, but I'm hoping someone like me might stumble upon this discussion now like I did yesterday.
