Installing acrylic / fibreglass bath

Have pulled out old cast iron bath and are currently installing a new one of same size but its an acrylic / fibreglass one. I have a couple of querries about the installation of these:
1. Where it is rebated into the stud wall, is this adequate support for that side of the bath (ie: stud every 450mm along the length of bath) or do they have to have support right along the side, which would require a batten built into the stud wall??
2. For the sand & cement mix under the tub, does this need an adetive such as bondcrete so the tub actually sticks to the mortar?

I have read the installation instructions but they have conflicting info and prefer hearing from peoples experience on installations.
Cheers


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