Toilets, Sinks, Showers, Tubs and Disposals - New Bathtub install

Just purchased a new tub/shower unit from Sterling (Kohler).
The instructions say place landscaping felt or mortar under tub.
They don't provide any instruction on how to do that- I called the manufacturer and they don't provide much help. With the tub in place it sits pretty level.
how much mortar should I spread under? Is the idea to get most in the center so the middle of the tub will "stick" in place more or less? I don't really need to level it- just provide a solid base for the tub to rest on

The mortar bed is not to stick it in place, but to give the bottom of the tub support in key areas. Good sized dollops of thinset in several places (except where the tub's support touches the floor) will do. Then set the tub in place and press it down so the dollops squeeze out somewhat.

ah ok - thanks- so the mortar should cover the whole "bottom section of the tub so to speak?

Ideally, probably, but 6 good heavy dollops will help spread the support out.

OK thanks..... so just a thin base will do? Most of the middle portion under the tub has tabs that touch the subfloor (which it needs to stay in contact with)- Would the mortar make it better or should I just leave it? The instructions say to put a pad there for less squeaking and mortar to hold it- I don't want to put too much down and push it up- Just enough to hold in place...

If you use thinset, it will squish out as you put pressure on it. It won't have enough consistency to bulge your tub up. And yes, don't put anything under the supports.