Just when you thought that Rice Krispies Treats had finally collapsed under all the baby-boomer freight attached to them, along comes Leaving Iowa.

Watching Tom Clue and Spike Manton's play, which continues its world-premiere run at the Purple Rose through March 13, is like taking a warm bath in midcentury Middle American iconography. Along with the Rice Krispies Treats and Iowa, Clue and Manton toss in a complete baby-boomer childhood time capsule: Sansabelt slacks, grueling road trips to impossibly dull places, Dad toting up the mileage, and Mom, God love her, always with that glazed smile on her face. What was she on, anyway?

The scenes involving all this boomer apparatus are played out in the memory of now-middle-aged son "Don" (John Lepard) as he drives through the Midwest with a canister of Dad's ashes on the seat beside him. Playwrights Manton and Clue have midwestern credentials, all right. They both went to college in, among other places, Peoria, and they presumably know, as few people do, what actually does play there. This oddly genuine yet emblematic detail of their biographies struck me as funnier and more endearing than a lot of the play itself.

Clue and Manton are first-time playwrights coming from radio and TV land, so perhaps this is a trial run for something with a little more depth. They have a grasp of scriptwriting techniques that have sunk other beginners: they know how to pace scenes, how to write dialogue that can be understood, how and when to introduce characters. But this was not a good choice of subject for a first attempt. You have to know where you're going with this material — the suffocatingly bland nuclear families of the period — because their story has already repeated itself as comedy, as tragedy, and as farce more times than anyone cares to count. For instance, Rice Krispies Treats stopped being the boomer private Proustian madeleine decades ago: you buy them now at the gas station, gigantic, factory made, with barcodes stamped on them. Leaving Iowa doesn't pretend to be more than a warm comedy, but it didn't warm me. It seemed merely a labored re-creation of a few weeks of a hyperconventional family's life.

I am happy to report that the playwrights do courageously break one long-standing rule of comedy. As we all know, when Dad's ashes are transported in an urn, someone is supposed to steal them, open the urn expectantly, and exclaim "What the — ?!" This does not happen.