Mortar bed under 1-piece Aquaglass fiberglass tub/shower
I am about ready to install my 1-piec Aquaglass tub/shower as part of a complete bathroom remodel. I know this has probably been done to death, but I'd like to solicit some advice about whether this tub/shower needs a mortar bed underneath. It is supported by (2) 2x4's on the underside that are attached to a piece of what looks to be 3/4" OSB. It appears that the entire weight of the tub rests on these 2x4's, hence the only place that looks to benefit from mortar would be under them. The instructions that came with the unit are silent about using anything underneath. I have attached some photos of the underside (tub laying on side). Please let me know what you all think would work best a trouble-free install. Thanks!