Could only get at a plumbing supply due to the size and they were over dollars more. I did use a can of Great Stuff foam to fill in under the base where it had a "little" movement. I was comfortable doing this, but you may want to enlist a professional plumber. My contractor loves this base and it should hold up well. Doing that there's always a chance of a little shift or movement and that what could cause a Leak. I recommend never to use drywall of ANY kind behind the tile, always use a tile backer board.
I use these all the time, I'm a remodel contractor.
Fiberglass Shower Pans
Make sure you have a level to make sure your slope is correct for the drain. We are very pleased with the service, delivery and unit! Really like the low rise curb. I use these all the time, I'm a remodel contractor. It may seem expensive, but considering the cost of a new shower, it makes good sense! Ease of installation, Quality and price. Also using flashing around perimeter behind sheathing to in front of flange makes a huge difference too.