Generally, a "pop up" boutique needs an established internet presence before getting started and some sort of hype... The only successfuly (and I do mean successful) pop up boutique I know of that has stuck around is
6% DokiDoki, and they're a pretty niche alternative fashion boutique that travels internationally and only stays in one spot for a month or so. But they have a permanent website, frequently updated facebook and other networking sites, "iconic" sales girls and strong networking with scenes and events related to the styles they portray. And they have a very, very eye catching set up whenever their shop "pops up". You'd never guess the shop was a temporary addition, its always colorful, organized and eye-catching. Which is essential to drag in foot traffic, given the short time the store will be present.
So... Since you're wanting to sell vintage... Maybe establish an Etsy shop, fashion & Vintage blog and such to accompany your facebook & twitter. And then network through websites and forums related to Vintage collections & fashions to gather a following and start the boutique online before hosting and advertising your "pop ups" on your networking pages & mailing list.