Wellington band the Windy City Strugglers have had the odd line-up change, but after nearly 40 years the core duo of Bill Lake and Rick Bryant are still spearheading a five-strong cast of blues-loving musicians.

In a commercial sense they should have gone to the grave decades ago.

In his documentary Struggle No More, Costa Botes tracks the band with a digital video camera as they write their 2004 album Kingfisher in a shabby house in the tiny central North Island settlement of Rangataua. There's also live footage of the band at Wellington's Circa Theatre and interviews with band members and music industry commentators.

The finished product is an affectionate and heart-warming story of persistence and passion - minus the success that often goes with those qualities.

Botes is no stranger to film-making, with credits such as Forgotten Silver (co-directed with Peter Jackson) and three soon-to-be-released documentaries on the making of The Lord of the Rings films. But for this project it was basically a case of getting a camera and following up on an idea when there was no way of telling how it could turn out.

"The theme actually saved the film," Botes says. "What kicked me off was the desire to make a documentary, given that I had some equipment, and it was just a case of finding a subject that I felt engaged by."

He says he thought following a band's writing process would be interesting, but the theme of passion and struggle - with little obvious reward - took its own shape.

"It was a little bit of a shot in the dark, because I didn't know any of the guys in the band and I had never listened to any of their music. What I did like very much was their name. I thought, anyone who calls themselves the Windy City Strugglers have obviously got a particular view on life."

That the band have been around for nearly 40 years and are still struggling along on a shoestring budget is a story in itself, Botes says. "For heaven's sake, they haven't even made a buck. Why do they keep going? That's always an interesting question."

He says when the filming began stretching out over a couple of years he started questioning both whether the project was worth it, and even whether his career as a film-maker was worth it.

"That got me thinking about the Strugglers again. There was this pile of footage sitting there and I thought, well, 40 years and they haven't given up ...

" And I'd formed a great respect for their music and thought, yes it's definitely worth what they do, even if they haven't made any money."

He put some more thought into how he could enhance the theme and did so by interviewing industry figures about the Strugglers and their story. "It was like the missing key to the whole thing really," Botes says.

In the documentary the band members talk candidly about what they do and why they continue. They either never wanted to be commercially successful, don't care, or many years ago became resigned to the fact that the big break was not likely to happen.

Guitarist Geoff Rashbrooke suggests there were other reasons he decided to play guitar in the first place. "This was a girl magnet ... but it didn't seem to work terribly well - there might have been other problems," he says.

With Bryant, one gets the feeling he accepted long ago that any monetary reward was unlikely. "It would certainly be an unusual event for us to have a hit record," he says.

Lake, a postman for more than 30 years, appears to have been put on earth to play blues music - nothing else really matters. His job, which the documentary estimates equates to two walks around the world, funds his passion.

He's tenacious, "but seems to have a philosophy that selling the music detracts from the honesty of its creation", Botes says.

He describes the Strugglers as "living treasures", and there are many others who love their music's authenticity. As American singer/songwriter Elliot Murphy said when he introduced the band at a gig in Europe: "For me it's deep blues from way down under, as if the Mississippi River had gouged its way through the centre of the earth and come home in ... New Zealand of all places."

The Windy City Strugglers seem to be gaining a small amount of traction with their music - if only decade by decade - having been backed by a French record label in recent times.

But some of the musicians now live in Auckland, others in Wellington, and have lives outside music to consider.

One gets the impression they won't put too much pressure on themselves to take on all the challenges the music industry might present.

* Struggle No More, Academy Cinema, Lorne St, Thu July 27, 6.15pm, Fri July 28, 10.30am