For a 4 foot opening, you should do a french door set up...two equal width doors on two hinges each. Say "no" to the channels. The less of this stuff, the better. Do not worry about leakage. French doors is the ultimate, you get two swinging doors allowing the ultimate in flexibility and ease of cleaning...swing each door out to clean, no more climbing around inside your shower to clean. I have 2 showers in my home with french doors and have no threshold gaskets or door gaskets, and the most leakage I have is equivalent to the amount a wet foot creates when you step out of the shower. No big deal, just leave a towel on the floor if that bothers you. This will pay back big time by eliminating channels and the silicone caulk. Super clean and fresh set up. I minimized my openings between both french doors and the walls to about 1/8".

@Lazygardens - I mentioned above we want to enlarge it to 36" W x 48"D or Deeper, but anything above a 36" Wide shower will make the closet in the bedroom we are taking the space away from not work. We are taking the large closet away from this room, and need to replace it with a smaller 48" W x 24" D Closet. As mentioned above does anyone know where I can find quality shower pans with the 36" side that has the entrance? I looked into having the pan be custom tiled, but I am worried about having long term maintenance issues regarding leaking and mold.

I have silicone and clips. The silicone is pretty much invisible. I guess the installers were careful. If you want to go frameless, why would you want a metal channel when you could have clear silicone? Find another installer.

Enduring- thanks for responding. I had seen your shower- it turned out just beautiful. I wasn't sure if in your research you'd explored a sliding glass door or not. To answer your questions. One end of the shower is on an exterior brick wall. The other is flanked by a custom linen closet surrounded by tile with the edges grouted. It's not coming out. If I had no other choice but to do doors, I'm pretty sure I'd have to remove tile on one or both ends and add the blocking- not something I'd like to do if I can avoid it. Likely I'd just have one door and a fixed panel on the other- I'm pretty sure the toilet clearance wouldn't let me do two doors like you have. Though I see your point about having a fixed panel- I can't drill into the shower pan so that wouldn't work either. Hopefully some of the glass guys can give me their opinion about using epoxy to secure clips on the bottom. Thanks again for your help- much appreciated. Lisa