Designing Kitchens and Bathrooms - Mortar bed for shower install

I am remodeling a bathroom and I bought a Sterling neo angle stall kit. In the instructions it mentions using a mortar bed for under the base, but there is little explanation. What type of mortar is recommended. My local hardware store carries MasterBlend standard thinset mortar. I was wondering if it would work. Also, it mentioned that it is important that all of the feet contact the subfloor. Willl I be able to set the pan on the mortar and shake it through till the feet contact? Or will I have to to make small openings for the 20 or so feet? This sems like a one shot deal so I just don't want to screw it up.

Mix up about 3 gallons of the thinset (to about the consistency of peanut butter) and put 4 globs (about 4 cups) equally spaced from the drain to each corner, about halfway. Then set the shower pan in position and wiggle it until it sits flush on the floor. The thinset will create a very stable base and alleviate any flexing of the base when you stand in it.

Thanks for your help!