I ran across an old thread I couldn't reply to but thought I would share my tile redi shower pan install experience, at least laying it down into the mortar. Seems like a lot of people in that thread had problems with flexing which made me worry quite a bit.
This was my first diy shower pan install and was on a concrete foundation. I ordered the tile redi trench (36x60) with the tile-able drain top and arrived from the freight company in a box that was pretty much open on arrival. Before signing for the delivery I inspected the pan worried it would be damaged due to shipping but luckily was in one piece. Probably best to get this from Home Depot/Lowes/etc if you can.
The pan itself is pretty light and as other mentioned felt cheap. It came with a 1-page instruction that I read over and over again. The shower area we are working in was accessible on both the curb and the back side (interior window) which made working with it for two people easier. The install called for type n or s mortar, so I used the Quikrete 60lb mortar mix type n from Home Depot. I bought 6 bags but ended up only using 4 of them. The instruction video that I found online from them looked like a different product than mine, as that product was more flat on the bottom and only recommended 1/2 to 3/4 inch of mortar. The product I was installing had deep ribs and the instructions said to subtract 1/2 inch from deepest rib, which ended up being 1 3/4 (not counting the curb's deepness which was really high). The thickness of the ribs was tapered from further part from the drain to shallow part around the drain. The instructions called for 1inch of clearance around the edges, so we built a 4 wall frame around the walls where the clearance would be, and then added some wood guides to indicate to us the height of the mortar (1 3/4 to 3/4 from deepest to shortest) we would pour. We mixed the mortar (milkshake) and poured the 4 60# bags of type-n mortar into the area and leveled it off based on our guides. After waiting roughly 20 minutes to let it firm up, we removed the outside frame. The mortar was firm enough to stay within the form we made but still soft enough to place the pan down. We primed and put the glue on the drain, lined up the pan and lowered it into the mortar. Starting with the drain side, we quickly tried to push the drain into place before the pvc glue sets (quickly). I would say we got half of the pipe within coupler before it was set. Looking back, I wish we made the pipe a little longer, but we feel comfortable that there is enough contact and glue that it won't leak.
We worked the pan back and forth/up and down and tried to get as much of the mortar up into the ribs as possible. IMO you'll never will get the entire voids filled with mortar as air will also get caught in there, but I don't believe that is the point. We could definitely see as we are pushing down, mortar is coming out on all four sides. The instructions call for the pan to be about 1/8 high with the mortar from the ground, but we were probably more like 1/4 (which is probably why the drain height was exactly as we predicted it to be). After leveling it, we let it sit for 24 hours. We never stood on it the entire installation process, which I feel is critical. I started reading this thread after the install and was worried about the flexing issue people were having and started to come up with my own fixes for it. The next day we stood on it and it is solid, no flexing. It will only get harder over the next couple days. When we start adding the redi proxy, tiles, etc, it will get even harder. We just need to be careful not to drop anything on the pan as we continue to work around it.
Looking back, it was pretty costly for what you get. The pan feels cheap/fragile, but it does harden up once you put it down into the mortar. I think you want to get the mortar up into the ribs as much as possible so that when the mortar dries, it expands and locks the ribs into place. IMO you don't need to fill the voids completely up with mortar before laying the pan. The drain was probably the hardest part even with two side access as the glue sets up quickly, so careful caution and quickness is needed for that when you don't have access to a subfloor.
It wasn't a terribly hard job to do, but for the cost of the pan I probably wouldn't do it again. If I do another shower pan, I would probably look at alternatives. But in the end, the pan did setup for me just fine (thankfully!).
Good luck on your projects!