Use plastic sheet above/below mortar when setting tub?

I am about to install a drop-in Hydrosystems whirlpool tub. Manufacturer requires a mortar seat. Floor is Sturd-i-floor ply; tub is fiberglas moulded onto OSB base. I am contemplating putting a sheet of plastic on the floor before shoveling on the mortar and then covering the loose mortar with another sheet of plastic before setting the tub on top. My reasoning is that (god forbid) if I ever need to remove the tub, it won't be stuck to the floor. On the other hand, maybe it would be better if the OSB was bonded to the ply? What do you guys/gals think?

Put it on both sides...the OSB will suck moisture out, weakening the mortar before it has a good chance to hydrate and cure.

Thanks, Jim. That's what I'll do.