Installing pre-formed shower base

I posted earlier regarding moving a drain for a shower. I'm getting ready to install the base, and am looking for feedback.

My base is pre-formed, and sits on a hunk of styrofoam to provide flex/support. I know this is not the preferred type of base, but this particular unit is the only one that will work for my tiny basement bathroom (I know people are going to post things like "that shower sucks, don't use it but at this point, it's either this thing or nothing). I purchased this AquaGlass shower at Lowes, and it's my understanding that all Aquaglass and ASB (American Shower and Bath) bases come with this styrofoam attached.

Here's directions if you'd like to look: http://www.asbcorp.com/manual/450025.pdf

What the direction do not tell me is how to secure the base to the floor so it won't move. My plan is to lay a bed of mortar on the floor and then set the base on top of the mortar. This will keep it set and keep any flex to a minimum. I was going to use based thin-set mortar that I used to lay my tile for this. Thanks in advance for the feedback.

Best advice is to exactly follow the installation instruction. I looked and it says nothing about bedding this in mortar. Sounds like mortar would prevent it from sitting level on the floor.

If the base is fully supported, AND the floor is flat and level, you may not need to anchor it...the walls and room floor will hold it in place. But, if you do want to anchor it, thinset would work...that is how some of the tileable bases are anchored to the floor. The size notch you use could give you a litle leaway in trying to level the thing if you use thinset, but keep in mind, thinset is not designed to be more than about 1/4-3/8" thick overall. Depending on the shape of the notch and its depth, you might be able to go as big as 1/2" square notches, but anything deeper would require a different mortar. Keep in mind, though, that you can build up thin layers and screed the floor to level if you need to...thinset will stick to itself, just don't get it too thick in any one layer and give it a day or so to cure in between layers, if you need to go that way.

It is a basement floor that is concrete. I put a lay of self-leveling concrete on top to give it a very level surface. Then, I put my tile down and am going to put the base down on top of that. My surface is very stable and level. I was just thinking of using the thin-set to keep the base from flexing at all. It is pretty flimsy, so I was concerned about moving a bit (not moving around, but just wiggling).

I emailed the manufacturer as well to see what they say. Since the directions are silent on the issue, I am curious if they would consider this "not following directions" or why they don't address it.

Ok, here is the feedback from the manufacturer, if anyone is interested.

"We do not recommend putting the base in mortar. The plastic needs to expand and contract and putting it in mortar may make it crack."

interesting.

Very understandable. The American Standard Americast tub has exactly the same instructions, probably for the same reason.