Dick,
Most installations of cultured marble bases, use either the mortar or fixall to level the base.

The important things are to:
Mark the floor for the trap center.
Set the base down to get the measurement for the vertical pipe that fits between the p-trap and the shower drain.
Remove pan, lay down the (fixall or mortar). Install pan, and wait for the (fixall or mortar) to set up before standing on the pan.

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