CHICAGO — Once a staple of the 1970s, the custom van has largely become a relic of drug-and-rock-'n'-roll-filled days past.

But for some, "vanning" is still a way of life — and a passionate one at that.

Humboldt Park-based filmmakers Andrew Morgan and Nick Nummerdor, both 29, took on the cult following behind the van as the unlikely subject for their first full-length documentary together, "Vannin'," which has a sneak preview at Portage Park's Patio Theater on Saturday night.

Morgan got a firsthand look into the obsession with vans when he bought his '73 Dodge van in the summer of 2011.

"I started really frequenting websites that catered to the van enthusiast," Morgan said. "That’s when I realized there was a lot more to it."

Morgan and Nummerdor decided to take his Dodge van to Elkhorn, Wis., in 2012 for the 40th National Truck-In, also known as the Van Nationals, the highlight of every year for self-called "vanners" who buy or rent vans that Nummerdor said are akin to their summer homes. There, the directors used the six-day event to capture the obsession and all its colorful personalities.

The subculture has changed quite a bit from what it was in the late '60s and into the '70s, when the vans were often associated with free love, psychotropic drugs and protest against the Vietnam War.

"It became a much more family-friendly thing rather than a bunch of wild teenagers in a field," Morgan said.

For its enthusiasts from all over the country, vanning combines a love for classic cars with camaraderie. Events like the National Truck-In allow fans and their families some time off to get together, listen to live music every night and keep a tradition alive, even if it is dwindling, the filmmakers said.

"The anonymity is kind of gone," as a result of the smaller attendance than in years past, Morgan said. "And it's created a kind of trustworthy atmosphere. Everyone leaves their keys in their ignition, everyone leaves their wallet out."

But the close-knit group isn't accustomed to much outside attention, the filmmakers said, and the idea of a documentary took some getting used to.

"At first, they were definitely wary," Nummerdor said. "They were like, 'Who are these guys?'"

But after bringing Morgan's van and meeting with the vanners to hang out and discuss the film, Nummerdor said the group soon welcomed them "with arms wide open."

"We were active participants as well as voyeurs," Morgan said.

The filmmakers said they set out not to parody the people they met, many of whom became good friends, but to tell their stories.

"We strive to portray them honestly," Nummerdor said. "For better or worse."

Some of the vanners plan to attend the screening, and a few of the custom vans will be parked in front of the theater. The film is mostly complete, the directors said, though they're adding some finishing touches. They're aiming to get their film into festivals in 2014.

Morgan said the film's soundtrack, which includes local band Heavy Times, Portland, Ore., rock band Danava and Minneapolis group Red Desert, is also a big highlight of the documentary.

"We made a lot of really great, honest connections," Nummerdor said. "Just meeting everyone was a really awesome experience, and some of those friendships that we made are probably going to endure past the film."

"Vannin'," a documentary produced by Little Cabin Films, has a sneak preview at 7 p.m. Saturday at the Patio Theater for $5 (cash only). A discussion will take place after the film.