PHOENIX -- A stack of shipping containers sitting in a lot in an industrial section of Phoenix has some developers thinking inside the box.

The structures usually used to transport cargo have been transformed into eight apartments. Scuff marks, old serial numbers and shipping company logos remain, but a look inside each unit reveals a 740-square-foot modern home.

"It doesn't even feel like a shipping container. It's also insulated really well," said Patrick Tupas, who is in the Air Force and along with his wife signed a one-year lease for $1,000 a month. "It just feels like a regular apartment."

In this March 16, 2016, photo, Patrick Tupas, with his wife Maria Real-Tupas, sit in the living room at their shipping container apartment in Phoenix.

There was a downside, he said -- passers-by asking questions and sometimes pressing to see inside their home.

Housing and retail projects using the containers have popped up in recent years in Las Vegas, Detroit and Washington, D.C., as developers and cities try to cater to millennials and baby boomers who want to live closer to the cultural offerings in urban hubs.

To meet those needs, "cargotecture" has become a quick way to fill urban housing gaps.

"They are faster, cheaper and now potentially have much more of an aesthetic range," said Dana Cuff, director of cityLAB, a think tank at UCLA that looks at architecture and urban growth. Some mask their shipping origins, but the ones in Phoenix don't, she said.

"They're celebrating them," Cuff said.

In the Containers on Grand project in Phoenix, the architecture firm, StarkJames, designed the apartments in a way that retained the corrugated metal exteriors. Each unit is made of two containers, but inside there are no signs of the cargo hauling days.

This March 16, 2016 photo shows a view of a shipping container apartment development in Phoenix.