The Gosselin crazy train is derailing big-time as “Kate Plus 8” lurches toward its series finale this Monday night.

This week’s penultimate episode showed a once-popular series in its death throes, with all the catfights, hissy fits and histrionics captured for posterity by unflinching cameras as Kate Gosselin and her brood took a two-week RV trip through the Southwest — on TLC’s dime.

In one particularly cringe-worthy scene, the shrewish Gosselin demanded a slice of pizza for her bodyguard, Steve Neild — telling one of her hungry kids to “eat salad” since Steve had “reserved the slice” the night before and “doesn’t eat” macaroni-and-cheese.

That, in turn, spurred a loud fight with the family’s simmering babysitter, Ashley — who announced she was quitting after being harangued by Gosselin for the umpteenth time on the trip.

“I’m so sick of your dramatics!” she screamed at Gosselin. “After this, I’m done!”

Later, out of earshot from Gosselin, she told the cameras, “I would die for these kids, but I can’t spend one more minute with her.”

The show has reached such unapologetic lows that CNN’s Anderson Cooper made fun of the “pizza incident” on his nightly “Ridiculist” segment — complete with “Kate Plus 8” footage.

It’s an inglorious end to Kate Gosselin’s reality career, which never recovered after her divorce from Jon Gosselin.

Their show, “Jon and Kate Plus 8,” was a reality-show darling after launching in 2007 with the aw-shucks, happily married couple rearing their large family in Pennsylvania.

But after a few seasons things between Jon and Kate went south and they became weekly tabloid fodder — which actually helped the show’s visibility.

In 2009, during the couple’s much-publicized breakup, “Jon and Kate” reached a staggering high of nearly 11 million viewers, a TLC record and unprecedented numbers for a cable series.

But once the network dumped Jon Gosselin, and the show morphed into “Kate Plus 8,” viewers fled in droves. Kate’s appearance on ABC’s “Dancing With the Stars” did nothing to drive viewers to her show, which was cancelled by TLC last month after reaching the 150-episode mark (for both shows combined).

Despite Monday night’s fireworks, and the show’s impending finale, “Kate Plus 8” has averaged only 1.1 million viewers this season — down 1 million viewers from last season.

Gosselin herself tells People magazine this week that she’s “really scared” about what her future holds now that her show is gone — but vows she will remain on TV.

“My family can’t be cancelled,” she says. “I want to stay in TV because I feel comfortable there; it’s an exciting life . . . this is too much fun not to find a way back.”

TLC officials had no comment yesterday.

But industry types say the writing’s been on the wall for some time.

“The show’s just run its course,” says one insider. “It’s just time. It’s done. They’ve done everything they can do.”