I like the work of Elderlemon design: http://www.elderlemondesign.com/
The book cover must attract the thriller fans. The fantastic elements may be suggested. The hero is no more a vagabond, so he wears jeans, a t-shirt and a leather jacket.
The cover may use symbols or be descriptive: I give you artistic license for that, provided it screams thriller and mystery.
The title of the book, Passager Clandestin (the Stowaway) must be a mystery for the reader until the last pages of the book: the reader must not know why exactly the book is titled The Stowaway. In his previous life, the hero, Vick Lempereur, has been a vagabond. He is able to see ghosts but can also be possessed by ghosts. I have already published a collection of short stories featuring Vick Lempereur, and provided the cover of the book, Le Vagabond.
For the Vagabond, I used the Parmapetit font, but I am ready to give artistic license for this. I also used the Bullpen Three D font for the name, but again, I give artistic license for the fonts.