Yeah bro I'm from Goose Creek, SC. I live right off the base. Look there are a decent amount of shops in the Charleston Metro Region. In Goose Creek there's the Kustom Shop. I've never heard anything good about them. Only really slimy stuff. So be forewarned with that.
In North Charleston on Rivers Ave across the from the Naval Hospital there's
Auto Sound Specialist... IMHO he is the absolute best there is in Charleston. Bar None. He's steep on his prices but you will walk away happy if you decide on him. That's why I didn't go to him to do my truck. But the owners name is chip lucas and the shop has trophies and articles from mags for its vehicles and installs all around the showroom.
Another quality installer is Custom Car Stereo west of the ashley. About a five minute drive across the bridge from Chip Lucas in West Ashley. Both of these shops have a stellar rep in the area and have been around for well over twenty years. Theres Nortons in charleston. They do quality work too and even have a show car at the shop (plus installs always going on) so you can seen their quality for yourself before you even walk in the shop.
Now there's also 360 Motoring and Unique (or something like that... its off of ladson road) both in ladson (about fifteen minutes away from the base) but they haven't been around long. There's another one that just opened this year on rivers before chip lucas (A small yellow building a bit before Siesta Motorlodge and Cox Auto Sales) but I don't remember the name. They really aren't a quality shop from what I seen when I visited the shop. Its small, all the brands are crap, and the install bay is a joke. Plus they just let folks hang around and beg in front of the shop and around the cars.
Hope this helps man but check them all out and get your own feel for the shops and components.