Eric Balfour's tattoos are actually his own, they aren't added to play Duke. The large one on his right shoulder is the work of famous tattoo artist Kat Von D, star of the reality series "LA Ink." She applied it in a 2007 episode of the series.
Two of the Douen are actually part of the Haven family. One is Olivia Wood, daughter of our VFX Producer Kris Wood. And another is Katherine Shore, daughter of Christopher Shore, who plays Haven psychiatric doctor-turned-coroner Dr. Lucassi.
The idea of doors leading to other worlds is also something seen in Stephen King's The Dark Tower series, first appearing in the second book, "The Drawing of the Three," when Roland came upon three doors that lead from his world to our own New York City. Each door was found standing upright by themselves in the middle of the beach.