I have a framed poster here that I'm about to hang up. It's dimensions are 27" x 40". And it's somewhat heavy. The frame is thin and there is no glass, just plastic, just to give you an idea of the weight. I'm about to mount it onto sheetrock, and there is no stud behind it. Nails or screws? That's pretty much what I have here...or is there something else I should use?