I'd build a wood tray that's extends 1" past the print washer on 3 sides and over the edge of the sink on the one. It can be raised on the end opposite the sink for drainage.
Given that it should not be holding standing water, I don't think you need to go to the extreme of fiberglassing the inside of this tray. Epoxy type paint should be fine. In fact, even enamel paint with caulked seams should be ok.