Ray, I've cuir buoillied lots of leather for my helmets, and it's extremely difficult to do that on anything thinner than 8 oz. The time/temperature window gets smaller as the leather gets thinner. It also narrows for thick leather that is floppy, and not very dense. I shoot for 175 degrees, and eye it like a hawk after a minute.
For thinner leather, I heat it at around 160 degrees for 3 or 4 minutes, time not being critical, then I oven bake it at 190 for about a half hour. The leather gets darker, and it scorches a tiny bit wherever it's touching it's supports. It also makes the leather tougher to dye, having some very hard areas. I don't think it would work very well for a scabbard. Too much distortion.
I've never tried wax because I've always gotten very good results using just water. Wax appears to make the leather even harder, but I've heard that that is deceptive, because on a hot day, the leather will soften.
What about drying the wet leather by forming it around a warmed up sword blade? It'd be the perfect mandrel.
Doug