I'm getting to put a shower pan on a wood floor which is unique in my part of the country.
The pan has cross ribbing which rest on the floor.
In dry fitting pan the two opposite corners rest a little high (1/32) from the floor
other than that pan looks great and level.

Questions:

1) Would it be best to use a mastic or silicon to attach the pan to the floor?
OR
2) Go with mortar between the cross ribbing to help support the pan?
3) If I go with mortar, should a moisture barrier (e.g 6 mil plastic) be
used under the pan to keep the plywood floor from degrading while the mortar
cures?

Thanks
David