Protect it like you would any other silver gelatin print. Toning with selenium isn't a bad idea, but I would avoid any sprays or lacquers at all costs. Most of them only harm archival stability, not improve it.

I would reconsider not using any glass if you want to keep the print for a long period of time. Contaminants will settle on the print over time and dirty it, and exposure to sunlight will cause fading. A piece of museum glass will greatly reduce the effects of UV exposure as well as protect the print from dirt and dust.