From what I've read about it, it sounds like an interesting phenom, but not too fun a place to visit. But..this is a great article anyway, with good stuff on Slab City. Here's an excerpt, read the rest here.
Go west, old man: where the American dream goes down the drain. (Letter From California).(Salton Sea, California)
Harper's Magazine, Nov, 2002, by Clara Jeffery
Several strange little human ecosystems have evolved around the Salton Sea, but none is as strange as Slab City. It lies four miles east of Niland, a dust bunny of a town below the lake's somewhat distended midpoint. During World War II, when great swaths of the valley became gunnery ranges and the crew of the Enola Gay practiced dropping dummy A-bombs into the sea, the Army opened Camp Dunlap, a mix of tents and wooden buildings erected on concrete-slab floors, between Niland and the Chocolate Mountains. When the army decamped in 1946, Niland recycled the wood into a church. Out in the desert, only the slabs remained.
Around the time that a prototype of the Mercury capsule was splashing down into the Salton Sea, squatters began to arrive at the Slabs. There was--and is--no electricity, no water, no sewage, no phones, but the slabs and the pockmarked roads provided a skeleton of a community, and anyone could camp there for free. Pioneers "Lucky Lady" and "The Mayor" started a CB roll call and medical service; soon the winter population of snowbirds and drifters was too large to count off and the roll call became an auction and a gossip show.
Entering Niland from the south, I pass the "Chamber of Commerce and RV dump" (a fenced-in dirt lot that hosts a weekly swap meet) and a downtown consisting largely of vacant storefronts. Three miles east of town a small butte marks the old shoreline of Lake Cahuilla, but geology cannot compete with what Leonard Knight has done to it. Using donated paint and mud adobe, Leonard has created an enormous Technicolor landscape--part Pennsylvania Dutch, part Pentecostal--called Salvation Mountain. The work's centerpiece is a giant heart containing the message: JESUS I'M A SINNER, PLEASE COME UPON MY BODY AND INTO MY HEART.
Slab City itself is an odd combination of mobility and decay. A gold-rush town without the gold. A pioneer town with satellite TV. Residents turn junk (and junk is everywhere) into shelter, into art. But this is a place where people come not to make something of themselves but to unmake themselves, or at least to leave their pasts so far back in the rearview mirror that it doesn't hurt anymore. Most have fled life's ordinary tragedies, but there are honest-to-God outlaws here, "people whose radar you don't want to be on," one resident warns.
To the casual visitor, the Slabs is a curiosity, one more stop on the see-America-in-your-RV tour. Next will come Yuma, or Quartzsite, or wherever the yen for mobility and a good swap meet takes you. But a lack of resources is the main reason people come to Slab City. A huge gaggle of elderly flock here because their VA and Social Security checks can't cover the cost of a $10-a-night RV park. They come because free is all they can afford, because it's warm, and a short drive to Mexico, where maybe they can buy the medications they need. And they come because although they treasure their independence they're scared of being alone.
(this is page 4 of about 10)