Twin Peaks went off the air three years ago, but some folks still can't get Laura Palmer off their brains. Since August 1993, Dallas-based publisher Craig Miller has been peddling Wrapped in Plastic, a fanzine devoted to ABC's deeply weird 1990-91 cult hit. ''People who were into the show when it aired are still really into it,'' says Miller, 35, who taps out the bimonthly on his home computer. ''There's even an annual Twin Peaks convention up in Washington State.'' Offering articles like ''The Log Lady Speaks'' and ''Twin Peaks and the American Literary Tradition,'' WIP sells about 4,000 copies per issue at $3.95 a pop. The magazine, available by subscription and in ultrahip comic-book stores, also contains features on semirelated fringe-TV stars: August's issue will sport a cover story on The X-Files' David Duchovny, who, as Peak freaks will recall, played the cross-dressing investigator who was assigned to check out Agent Cooper.