She wouldn’t go anywhere without a hotel reservation. Now, she’s nagging to get back on the road.

Some of the 33 years Mueller spent with aerospace firm Hamilton Standard came at Texas’ Johnson Space Center, where he helped develop the portable life-support system worn by Apollo astronauts on moon missions. But “space age” suits the vehicle Mueller and his wife use on return visits to the US from their home in Sydney, Australia: a 40-year-old GMC Motorhome.

A sensation when General Motors introduced it in 1973, the Motorhome attracted a fervent following that endures in its US homeland and in far-flung corners of the planet, 37 years after production ceased. Such single-model devotion, customary in the collector car realm, is rare among recreational vehicles, or RVs.

As with classic cars, GMC Motorhome ownership bids one passage into a club, its members united by the common desire to keep their occasionally temperamental machines viable. Owners, known as “GMCers,” tend to be of retirement age, and travel in their decades-old RVs for weeks or months at a time.

Related: The joys and sorrows of full-time life in an RV.

This loose but supportive community convinced Mueller that keeping Motorhomes on two continents would not be a reckless endeavour. Born in the New York City suburb of Hoboken, New Jersey, Mueller retired in 2002 to Australia at 55 with Helen, his Australian bride. The couple bought their first GMC in 2007, having grown weary of summer touring on a Harley-Davidson. GMCers name their coaches, and Mueller calls their Australian RV, which has been converted to right-hand drive, the “Blue Streak.”

Mueller bought a second GMC in 2008 in the US, sight unseen. By remarkable coincidence, it was just two serial numbers removed from its Aussie cousin, and both had been up-fitted by trailer-maker Avion.

“After nearly 40 years, what were the odds?” he asks.

“Astronomical” seems appropriate. Mueller named his US-based coach “Double Trouble,” making numerous mechanical and interior upgrades. He and Helen tour the US west and southwest in the GMC from June through September.

Espen Heitmann, one of the many GMCers who Mueller has met through the GMCnet online community, lives in the postcard-picturesque village of Eidsdal, Norway, population 400. Heitmann, who at 46 is by his own estimation among the youngest of GMC owners, restores 1960s and 1970s GM vehicles as a hobby. For a time, he owned two of the five GMC Motorhomes he believed to be in Norway. At Mueller’s suggestion, Heitmann named his second GMC “Double Trouble,” translated to the Norwegian: “Dobbelt Trøbbel.”

This “Dobbelt,” however, was just a stop on the way to purchasing and restoring yet another GMC named “Big Green” for its original, very ’70s Parrot Green colour.

“I’ve had this GMC for three years and used it for vacation last summer with my girlfriend of 25 years, covering 3,500 miles in three weeks,” Heitmann says of Big Green. “Before that, [my girlfriend] wouldn’t go anywhere without a hotel reservation. Now, she’s nagging me to get it back on the road.”

Sleek and even sexy by RV standards, the GMC Motorhome was just as radical beneath its wind tunnel-shaped body. Key to its low height, easy handling and smooth ride was a chassis that used the Oldsmobile Toronado sedan’s front-wheel drive powertrain and a novel four-wheel rear air-suspension system that obviated the need for cross-vehicle axles. The floor was just 16in (406mm) off the ground, and a low centre of gravity helped the GMC, which was offered in 23- and 26-foot models, handle with surprising composure.

The Oldsmobile 455 cubic-inch gasoline V8 engine provided plenty of low-end torque, and the good aerodynamics helped the GMC achieve 11mpg highway fuel economy – better (which is to say, less dismal) than the 7mpg to 8mpg typical of the breed.

The GMC’s construction – comprising aluminium and sheet-moulded compound skin bonded to an aluminium superstructure – was more aligned with aircraft than the period’s RVs, most of which were essentially wood-framed boxes on commercial truck chassis. The panoramic windshield and large side windows also distinguished it on the highway.

The GMC Motorhome started at $13,600 in 1973 in the US, but exceeded $40,000 by the end of production in 1978, depending on model length and options. Amenities could include central air conditioning and heat, microwave oven and gas range, colour television, built-in vacuum cleaner, AM/FM stereo and cassette player and a citizens’ band (CB) two-way radio, all powered by a 6,000-watt onboard electric generator.

The GMC’s rust-resistant body and its devoted following have yielded respectable survival statistics. Of 13,000 GMC Motorhomes built, 8,450 are listed on a website, known among GMCers simply as the Registry, managed by John Shotwell of Archbold, Ohio. He and his wife, Pat, bought their 26-foot 1976 model nine years ago.

“I’d wanted one since they were introduced,” says Shotwell, 74. “Our longest trip so far was around the Great Lakes for about two weeks, and about 2,200 miles.”

The couple are rebuilding the GMC’s interior and, like many GMCers, are doing the work themselves.

The Registry does not account for vehicles’ operational status, but an estimate of several thousand Motorhomes still in active use seems reasonable, according to Bill Bryant, historian for the GMC Motorhomes International (GMCMI) club. The IBM retiree, from Pleasantville, New York, has exhaustively studied and documented the GMC. Bryant and his wife, Nita, have logged more than 200,000 miles over 31 years in a 1976 model. Their GMC has been treated to aftermarket fuel injection and a quad-bag rear suspension, among other readily available upgrades.

Most GMC Motorhomes sold remain in the US and Canada. Meanwhile, Australia, Germany, Britain and the Netherlands each have at least a couple dozen, according to Registry statistics. In Veldhoven, the Netherlands, Ruud Ledeboer rebuilt the interior of a 1977 GMC bought in 2007. He and his wife, Thea, have spent as long as a month on the road in it.

“The GMC keeps us young and free,” Ledeboer, 59, says, offering as succinct an explanation of the Motorhome’s enduring appeal as any.

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