It depends if they are really static or you want to have some dynamic parts in them. For example, if you want to share the layout (including partials, rails helpers and assets) of the rest of the website, you probably won’t go with the public folder.
Found this stack overflow answer, which is a great recap of the different approaches:
https://stackoverflow.com/a/43399855/1460504
It refers to a plain Rails application, but I think it makes perfect sense for the Solidus context as well.