Cultured marble shower base over plywood: Do I need to nest in a bed of mortar?

I am installing a 48x34 inch cultured marble shower base over a clean, level plywood subfloor. Is it necessary to nest the base (a pretty heavy one) in a bed of mortar?

Also, are there any tips/methods/suggestions for getting such a heavy base into place safely in a small bathroom using only two guys?

If the floor isn't perfectly flat (almost none are) or if the bottom of the base isn't fully seated on the floor, then bedding it in dryset mortar, plaster of paris means that it might flex or rock. If the manufacturer recommends it, do it. Practically all will work better if you do. My unprofessional opinion.