Another way to deal with an untreated room is to hang a bunch of a moving blankets in a corner, and/or fill it with whatever kind of padding you can (a small mattress or couch cushions), then put the mic a couple of feet in front of the corner. Have the talent face the corner as they deliver their lines.

You can also stand up a sofa, and face the inside of that.

In my opinion closets suck up too much high end, and sound too dead, when you really just want to avoid too much room tone without killing the frequency spectrum of the voice.

A cheap way to treat a room is with bookshelves. Make sure the books are at random depths. I have one in a corner at an angle. It acts like a diffuser as well as a bass trap.