What does a dirt-filled hole have to do with this project? This is the first problem I encountered. Where was the plumbing? It was buried under 8" of dirt. I spent a whole day digging it out and then cleaning out the drain pipe I eventually found .
The second problem I had was having to build the back wall out 3 inches. 2x4's and plywood did the trick.
Here is one with the fiberglass shower pan visible.