mtcummunins, do you use thinset alone to do the kerdi membrane and base or also chaulking that JW is talking about? Do you use preformed shower curbs and benches or build your own?
I'm not sure what you mean by "thinset alone," but i like the schluter base, thinsetted down to the subfloor, then kerdi installed over that. I haven't built any huge showers, mine have pretty much all been 30-32" wide, but what I like to do is use basic roofing principles with the kerdi... start at the bottom, run the kerdi horizontally through the corners w/o seams, and overlap the edges bottom to top. This relies very little on the thinset for waterproofing, only wicking can get water past the seam. It does make the overlap area thicker than using the kerdi band, but i prefer this system. Alternatively, you could put the sheet on the wall, band over the edge and up onto your backer board, then bring the next sheet of kerdi down to the top edge of the lower sheet (rather than putting the band on top of the seam, you're lapping it like a roof). This would save you some thickness.
Anyway, back to the width... one of the things that narrow showers lets you do is run the floor piece up the walls... i center the bottom sheet w/o cutting it to width, cut out the corners, and run the edge of the 39" sheet a few inches up the wall on all edges. Then I add the corners, then bring the first wall sheet all the way to the bottom of the wall. You have to get those corners in tight (squeeze out a bit more thinset than normal), or the buildup can be too much. Again, this is roofing style... don't count on the thinset seams much, but rather the lapping of the sheet.
It is difficult to manage a sheet long enough to wrap all the way around the shower, but its worth it to me to not have seams in the inside corners.
I have used the preformed curbs mostly, but I don't think they're necessary if you do a meticulous waterproofing job. You could just as easily, and much more cheaply, build your own. But, the extra time to do that isn't really worth it to me, so I generally just get the $50 curb in the kit and use it. I've not used any of the pre-made benches. I've always had very specific requirements for them, so I like to custom build them. Same thing with niches, they really need to be custom built to be able to get exactly what you want. I'm sure some of the bench options out there are good ones, but you don't want to ask me about that, as I don't have any experience with them. For example, the shower I'm doing next is 5 feet long at the shower pan, but then steps up for the bench, and out an additional foot. This space is suspended over a staircase. Its a maximizing space move, and one that has to be custom made for the application. It's also critical that the bench then gets completely waterproofed, as its not over a pan anymore...
I like the valve seals and such they offer as well... keep it all sealed up tight.