Robin Williams' latest Hollywood vehicle has its own kitchen, sleeping quarters, luggage compartments and toilet, where the studio should have flushed the script the minute it crawled through the door.

The vacation romp RV sucks the "recreation" out of recreational vehicle, offering a few very scattered laughs amid a relentlessly unfunny road trip of bad slapstick, shrieking performances and enough feces gags to make constipation sound like a viable lifestyle.

And this from director Barry Sonnenfeld, who first made his mark as cinematographer for the Coen brothers and directed The Addams Family, Get Shorty and Men in Black. Considering Sonnenfeld also made Wild Wild West and Big Trouble, it's no small feat of mediocrity for RV to be his low point.

Other than the animated Robots, in which he supplied supporting vocals, Williams hasn't had a hit since Patch Adams.

With even mediocre family films proving one of Hollywood's steadiest draws lately, Williams must have figured cloning and toning down Chevy Chase's National Lampoon's Vacation was a wise career choice to allow him to keep making things like House of D, The Final Cut and other little films no one wants to see.

Truthfully, the idea of Williams as a madcap dad leading his reluctant family on the RV sojourn from hell sounds like a giddy, goofy way to let a carefree 90 minutes pass.

Yet other than occasional glimmers of witty dialogue, the script by Geoff Rodkey (The Shaggy Dog, Daddy Day Care) amounts to four flat tires and a busted radiator hose. Lame jokes and sight gags are repeated so often you feel you're driving in circles.

The story is built on a clumsy premise to put Williams and family on the road. Williams' Bob Munro, a frazzled marketing ace in danger of losing his job at a soda company, scraps his clan's dream vacation to Hawaii so he can spearhead his boss's pitch meeting to take over a family-run soft-drink operation in Colorado.

Without telling them the real reason for the trip, Bob sells his wife, Jamie (Cheryl Hines of Curb Your Enthusiasm), and their kids (singer Joanna (JoJo) Levesque and Josh Hutcherson) on an RV trek as a way to rejuvenate their family ties.

Standing in as sort of the Randy Quaid, annoying-cousin character of the Vacation movies, Jeff Daniels expends much of the goodwill he earned from last year's brilliant performance in The Squid and the Whale.

It's depressing to see Daniels waste his time in a painfully oafish turn as a good ol' boy who lives on the road with his perky wife (Kristen Chenoweth) and their kids in a modified bus (Sonnenfeld's daughter Chloe plays one of their children).

Hines and Chenoweth come away comparatively unscathed, managing to inject a little warmth in their pleasantly bland wifey roles.

Considering his resume includes Death to Smoochy, Williams at least may not have sunk to a new career low, but RV puts him an embarrassing notch or three below Steve Martin's bumbling dad in the Cheaper by the Dozen movies.

Along with endless tumbles, falls and spills, Williams is called on to take a fecal shower, feign diarrhea in the woods and spend a good chunk of time either perched on a toilet or searching for one.

Besides a brief moment toward the end, Williams' gift for manic vocal patter is wasted on exchanges either tedious or shrill or both.

After all the disharmony and crudity, RV inevitably arrives at a saccharin message of family unity. But you feel like road kill getting there.

One and a half stars out of four.