The biggest issues I had with coating canvas with emulsion was processing chemicals getting trapped behind the emulsion, by soaking in at the edges and through the back. Canvas has an easy fix of course - size it and prime it well, and if necessary put a coat of poly on before the emulsion. Essentially you're making sort of an "RC canvas", where processing chems can only get in through the emulsion surface.
For chamois leather, priming is out - OP could experiment with soaking the leather in PVA sizing though, which would stiffen it, so you'd want it to dry with the folds/wrinkles/whatever that you want the final to have.
Been thinking of emulsion on brown kraft paper, with the highlights of the image first painted on, so similar problems would ensue. Haven't experimented with it yet though.