He's a costumer's nightmare and a musical director's dream. Seth Mrowka stands 6-foot, 7-inches — not what you'd call an easy one to dress — and sings with a rich, controlled voice "in the basement" according to Craig Faulkner, who directs him in Seacoast Repertory Theatre's current production of "Forever Plaid."

"There's a lot of people that have a richness, but not the bottom end he has. He hits the low notes and sounds like a tuba. It's just that natural, rich bass sound," says Faulkner, who shares the stage with Mrowka in "Plaid."

"I've never met anyone that hits them as effortlessly as he does."

And there's more, says Faulkner. Mrowka came to rehearsals nearly off book.

"It was incredible. He was helping us out," says Faulkner. When it came to the show's choreography he quickly mastered his steps and everyone else's.

"He bails us out when we're confused," Faulkner says with a laugh. "We're fortunate ...; to have Seth."

The plaid tuxedo and thick-rimmed, Buddy-Holly style glasses he wears, along with the goofy persona he portrays as Smudge, certainly play up his long and lanky look for its humorous side. Smudge is what you'd call geeky. Mrowka pulls it off well. But when he launches into "Rags to Riches" — even with the glasses — the geek is gone.

There's no dweeb present as he mills around talking to the crew and cast during rehearsal breaks, just days before opening. Instead his demeanor is self-assured, congenial and sharp.

Faulkner swears the man has a photographic memory.

"Not for dance," says Mrowka laughing. "Music; I can generally see the markings, the layout on the page ...; what's coming next by where it's situated on the page." Ditto for monologue. But Mrowka shys away from the photographic label — after all it can take him a few times looking at the page to record. — Poor guy.

Mrowka, a Littleton native, graduated from the University of New Hampshire with a musical theater degree in 2001. (That memory of his helped a lot, but not with math, he says). After school he headed to New York City to try his skills in the big pool; he's been living in Astoria since.

Till fairly recently Mrowka held only disposable jobs and went the ongoing-audition route. There were shows, "from Arizona to Alaska," he says, but no big break.

When Seacoast Repertory Theatre called, Mrowka had semi settled into a comfortable bartending position in the city. He's already sure he won't be heading back to the job-with-bennies when "Plaid" is done. SRT has sort of "jump-started" things, he says. It's back to every-day-audition mode.

"There's not much else I want to do in my life. That's why I was doing a bar job, there's no real commitment," he says.

But even working for the bennies he hadn't abandoned art. He studied voice and took audition classes — honing his craft before the next assault.

Mrowka was familiar with SRT before it called; classmates had performed there. So when he got the call he jumped at the opportunity, as much for the part as the place. "This is one of my dream shows and roles," he says. "I've always loved really tight four-part harmony. I did a cappella in college. And this is non-stop, four part." He knew his physical frame could add to the character; "so it all fit really."

That frame of his has occasionally proven a "make or break it" element in casting.

"I know in two separate instances where it was a part of the casting decision; I got one because I was tall," he says. "And I didn't get another because I was tall."

He feels he could take anything on but finds he's often cast in character roles — humorous ones.

"Compare me to someone standing next to me and that's already funny," he says. "But in style, I go for the innocent kind of a role — like Smudge." He's played Big Julie in "Guys and Dolls," and Rooster in "Annie" "and I'm always cast as the older character."

Mrowka's casual, warm demeanor, great smile and expressive face lend themselves to broader use. He hopes with time he'll get to prove that. He intends to keep trying.

"If there's something else you want to do and could be happy doing — do it instead. But telling an artist that doesn't have weight. ...; This is all I want to do."

So next?

"We'll I'd like to audition for a show up in Manchester, but after that move back to New York City. I'll try the starving life again, cater and temp work while I audition," he says. "I want to keep this momentum going as a working actor."