What I would do, is not even worry about dry mounting. You can get linen tape, or if it's just for yourself, you can use artist's tape (it's like masking tape, but the adhesive isn't as strong) and just make a "T" mount to attach the photo to the backing board. Then just put that behind your mat. I assume your mat has a bit of an overlap on an 11x14, so the mat will hold the print flat.