There is more info in the plumbing forum, but as for the concrete make a square form out of 3/4 boards toe screw from the inside for removal. Be sure to get the pipe level and plumb, put 4" concrete in the bottom of the hole too so the pipe won't move in the fitting and leak below ground you should end up with a nice neat square hole with a concrete bottom about 10" x 10" and 4" deep. Check the fitting on the shower to see for sure how deep the hole should be, I think yours is built in and can't be changed, I hope it is the gasket type, like the retrofit shower, and not a glue fitting. Make sure the pvc is high enough, I leave it too high and cut it from the inside with a dremel tool after it comes up through the fitting on the shower base. Read my posts in the plumbing section for more.
Let us know after install how you like the swanstone for use and cleaning.