Alright. I got some more sections of cellular core pipe from OSH, along with some ABS cement, and 1.5"x1.5" couplers. At the Dublin Lowes, I picked up some of those automotive clips as shown in the pic you provided Mark. I got the 1/4" clip screw in pin vs. the push-in pin. I also picked up some of those Cobra Triple Grip anchors, as shown in the link I provided, to try out.
I did a dry run on some extra ABS pipe I had. Quartered the piece of ABS pipe so I could use a quarter as my fastener on top of the cellular core pipe. With regards to the auto clips, I drilled pilot holes progressively getting bigger until I used the 13/64" drill bit. That seemed to work for my pilot hole b/c I was able to push the auto clip in, but I was not able to drive in the screw-in pin. Despite that, the auto clip did seem to give a pretty secure fit. I had to exert some good pressure to pull it apart. Thus, I think if I had enough of them spaced over the pipe that this may work. But, I think I will go back to Lowes and get the 1/4" auto clip with the push-in pin. Hopefully, that design would work and allow me to push in the pin.
I next tried the Triple Grip anchor. It worked to secure the pieces together, but it actually allowed a little play between the quarter piece and pipe when I pulled on them. Since this is meant as an anchor on a wall surface, I see it wouldn't work b/c the pipe and quarter piece together are too thin to be able to engage the wings on the anchor.
Lastly, I realized why not just drive the screw that came with the Triple Grip wall anchor in the quarter piece and pipe. It's was a #8 1.25" screw (most likely sheet metal screw). Drilled a pilot hole, which I probably did not need to do, drove it in, and it held great; the best out of the three tests.
I am thinking that the best, and easiest, would be to just use some stainless steel sheet metal screws to fasten all this. If I drive it in easy, it should be fine and won't crack the pipe. Let alone, if I am really concerned, I could buy some metal, or even nylon, washers. But, I don't think they are needed. Also, I don't see any problem with getting a stainless steel screw. It shouldn't react w/ the pool water, and it should be able to resist any corrosion good enough.
So, why not just use some stainless steel sheet metal screws, such as these
http://www.lowes.com/ProductDisplay...&catalogId=10051&productId=3811423&cId=detail or these
http://www.lowes.com/ProductDisplay...51&catalogId=10051&productId=3811425&cId=list, instead of those automotive clips (of which it seems that the only feasible one would be the push-in pin design)?