Thanks Reach4. Yes I am just dry fitting everything first. Next I will be laying a 2" bed of mortar to set the tub. Also is it a good idea to put a piece of plastic bag between the mortar and tub?
I am bothered by the word "bed". Search this forum for
mortar piles.
You don't want anything similar to a flat bed.
Mortar dollops, I would picture about twice the diameter of the gap, can go in plastic bags, or yes, you can put plastic under and/or over. You want the mortar to squish, and you want to have space for it to spread out while squishing. Mortar does not need air to harden, and it is better if it does not dry out soon.