In most cases, I don't think you need to treat the paper, unless you think your ink may rub off with handling. My Epson printer (now deceased
) used water-resistant inks so I never did anything else to the printouts. If you
do decide to give them an overspray, I would recommend something like Grumbacher's Myston Workable Fixative. It's designed to be used with pastel, charcoal and pencil artwork so should work with inks. I'd still test it on some scrap, though, since I haven't tried it myself. I got a (recommended) can for use with pastel weathering on my Sierra West Backwoods Log Train, since it apparently does not dissolve the pastels.