Where do I put it?
Folks always seem interested in the best way to mount DCC systems in, under, and around layouts. The most common position for command stations and boosters seems to be the simplest, sitting on a shelf below the layout. This arrangement is quick and easy, plus it makes wiring and access fairly direct. However, it can make it difficult to see the lights and hear the warning buzzer sounds, especially if you have to count them to figure out what is going on. It also makes the components prone to accumulating dust and scenery materials.
Personally though I prefer something up front or on an isolated shelf. Lining up your command station and boosters next to one another greatly simplifies connecting them together. However it does mean that all your wiring must fan out from some central location and therefore can mean long power bus runs to get to those far flung portions of the layout. The other option of course is to place your boosters near the section of the layout they power. This results in short runs but it can make it more difficult to debug problems between boosters.
I have one friend who has his DCS200, power supply, and PSX3 stashed safely away in an old stereo cabinet under the layout. The cabinet still has the old clear plastic doors which prevent dust and scenery materials from building up on the components while still allowing him to see the lights on the components. Some of these old cabinets even had fans to cool components, but you can also add an old computer fan to do the job. These are easy and cheap to find at yard sales, junk stores, and on Craigslist.
Another friend placed his DCS50 in one of the bins on the control panel he originally built for dual DC cab control of his layout. This is a neat solution since the DCS50 has a built in throttle that can be used by a yard switcher. On yet another layout the command station and a booster, along with their transformers, are placed in cutouts in the fascia in the sections of the layout they power.
On my Piedmont Southern I built a wooden box with a clear plastic door to hold my command station, booster, power managers, and power supply. I also cut a hole in one end where I mounted a small computer fan which keeps the components cool, preventing thermal overloads. Once the lower deck is finished I plan to hang it from the upper deck supports and install the lower fascia around it creating a built-in appearance.
So there really are no rules, just do whatever suits your situation. However I do have a few suggestions, (1) try to enclose the components to prevent dust build up, (2) consider installing a small fan to prevent heat build up, (3) put it up front where you can access it easily, and (4) on large layouts place each booster in or near the section they power. Finally, a safety warning. Please don’t leave exposed transformers out in the open. I have seen this on several layouts and even at train shows. All it would take is one curious child touching an exposed 110VAC connection to put an end to your model railroading. If you’re lucky the kid would only get a nasty shock, but it also could be deadly.