There goes the neighborhood!

Motor homes have invaded the Upper West Side, sparking fear in the hearts of residents worried their well-heeled haven could fast be transformed into a low-rent campsite.

“Why is this ugly piece of junk here?” demanded area activist Gretchen Berger, referring to the rusted RV that has been stationed at Riverside Drive and 74th Street.

“It just sort of creeps me out that somebody is living in a parking space, and this may give rise to other people thinking that it’s a cheap way to live on the Upper West Side, where the rents are high. Is Manhattan going to become a trailer park?”

The RV — an ’84 Chevy Pathfinder — belongs to Queens-born Rabbi Steve Blumberg, a Kabbalah practitioner, who told The Post his neighbors need to lighten up.

“If you want a gated community, you should live in Creedmoor [Psychiatric Center],” he said. “Otherwise-liberal West Siders have very serious middle-class scruples about what should or should not be in their neighborhood.”

Blumberg, 62, has been living on and off since 2007 in his RV, which he scored for $8,000 on eBay from a South Carolina resident.

“I lost my apartment in Riverdale, and at that moment I wasn’t sure about where to rent and how much to spend and all those things,” Blumberg recalled. “It just occurred to me that perhaps I could have a mobile studio apartment, so I started shopping around.”

The red-bearded rabbi took a Post reporter out for a spin in his RV — named Bessie — which lurched to a start after several attempts to get her going on a frigid Thursday morning.

“She starts and runs like a top,” he boasted as he rumbled up Riverside Drive to 79th Street.

“It is so well designed that I can spend days in here without getting claustrophobic. It really is apartment-size,” Blumberg said. “I’m in way better shape than the people who are renting closets.”

Blumberg, who said he’s now staying in a rent-free pad on 74th Street, also uses his 23-foot vehicle as a crash pad for visiting friends, or as a space to collect his thoughts, meditate and pray.

“I think the greatest thing about it is having the comfort of sleeping in a real bed, while being, at the same time, in the middle of everything going on on the street,” said a 54-year-old friend of Blumberg who shacked up in the RV while visiting from Romania last summer. “I could hear the bus, the cars, people walking their dogs, passersby talking, police with the sirens on. It’s even more special, this being New York.”

Blumberg said his RV — whose roomy interior features a SpongeBob SquarePants comforter and a sit-down tub — has never been ticketed but he confessed to being unsure of the law.

Leaving a mobile home on a city street for more than 24 hours is illegal, according to a Department of Transportation spokesman, who cited a traffic rule that also prohibits parking boat trailers in the same spot for more than a day. Enforcement is typically complaint-driven. Fines start at $115, the NYPD said.

Farther uptown, on Central Park West — where the neighborhood’s most expensive rental, a town house with a pool, fetches a cool $75,000 a month — stands a 19-foot, 1975 Dodge Sportsman with gold rims and two cameras affixed to its exterior.

“It looks like it would fit more in the mountains of West Virginia than on the Upper West Side,” said area resident Ron Hoffman.

The Dodge owner, who only gave his name as Robert, refused to answer any questions.

Neighbors are puzzled by the RV’s windows, which are covered by gold curtains.

“He once told me he just uses it to store things — but if that’s the case, why would you have everything blacked out so you can’t see the person inside!” said longtime resident Bill Smith.

“I don’t think it should be here,” added Mario Parisi, 86. “We’re all waiting to park. Sitting there all the time is not a good idea — it’s a monster.”