I try to avoid dry mounting and use archival corners on 4 ply acid-free board with a 4 or 8 ply overmat. The metal sectional frames come in different sizes some of which will accommodate the two 4 plys, foam core and glass. There may be some that will hold 8 ply as well but you may have to mount the print on 2 ply board and compress the foam core as mentioned. For wooden frames I use a frame shop.

http://www.jeffreyglasser.com/