Nestled within the city of Madison, a sub-city has erupted — a gleaming, aluminum Silver City.

Some 900 bullet-shaped trailers made by Airstream are populating the parking lot of the Alliant Energy Center and will stay there for the next week.

Practically self-sufficient, the Silver City has its own postal service and newspaper carrier; its own electricity, water service, security detail, and even a government of sorts.

The group — The Wally Byam Caravan Club International — is here for its annual international rally, which meets in a different city each year and has never before been in Madison. The event officially started Sunday.

By the time the group leaves, it is estimated it will have pumped half a million dollars into the local economy, given stuffed animals and warm clothes to needy families, and donated gallons of blood to the Red Cross.

The Airstream trailer is more than 75 years old, designed by Wally Byam, who wanted to create a trailer light enough to be towed by a standard automobile but one that would offer all the comforts of home.

The result was the iconic, Twinkie-shaped trailers and a cult-like following of fans, willing to travel great distances to be among other enthusiasts. Group members like to point out theirs is the world’s oldest trailer or motor home organization.

Take Patti Reed, 59, from Lafayette, Colo. One of the first things she’ll do when you meet her is proudly show off the Flying Cloud tattoo on her shoulder. Flying Cloud is the model of her 1953 retro trailer, named Pearl, after its first owner.

Reed said she first got interested in the group when she was 50 and going through a mid-life crisis. Looking to buy a camper, she stumbled across Airstream in the newspaper classified ads. She was soon hooked on the brand, especially the vintage trailers. Her trailer is decked out in 1950s decor down to the toaster.

"There’s a pride in having an old trailer. When we’re on the road, people follow us off exits," she said, sitting in a lawn chair outside her trailer with a flamingo-shaped ashtray beside her. Pink flamingoes are big among Airstreamers.

The group is mostly made up of retirees. It helps to be retired if one is to have the time to drive across country and set up camp for weeks on end. That means there is some concern about keeping the group’s flagging membership. This year’s rally drew fewer trailers than expected, but that could also be due to the recession and the cost of fuel.

Still, the group has about 6,500 members, although not all attend the rally.

Since the trailers double as homes, they come in a great variety of models and trappings, as members attempt to creatively fit their lives in spaces that range from roughly 19 feet to 31 feet long, depending on the model.

The club boasts that 60 percent of all Airstreams built are still in use, which means there are dozens of vintage trailers on display at the rally.

Herb Spies, from Fort Walton Beach, Fla., owns a 19-foot 1963 Globe Trotter and teaches a class on polishing the trailers — one of the many seminars offered to Airstream aficionados during the convention.

He said it takes him about two to three weeks each year to buff the aluminum exterior to a premium shine, measured in some circles by whether a woman can fix her make-up in its reflection.

Many of the Airstreamers say what they like most about the rallies are meeting people and maintaining friendships.

Patti Reed, the tattooed maven of Airstreams, even met her husband at a rally in 2006. At that time, between the two of them, they had five Airstream trailers.

"At this age, you don’t think you’ll run into someone who has the same passion for something as exotic as this," she said.

IF YOU GO

What: Open house for the general public at the Airstream rally.
When: Saturday 10 a.m. to 3 p.m.
Where: Alliant Energy Center parking lot.