I have dry mounted two posters to opposite sides of 1/2" Gatorfoam, along with heat-activated PVC laminateing film, such as Bienfang Finish Guard.
I stock Gatorfoam in white and black, both of which look OK when the edges are neatly trimmed. For hanging, I suggest using long nails pressed into the foam on each side, with #2 stainless steel wires extending to the ceiling. This way, it is easy to hang it straight and level.
If fading of the posters is an issue, I suggest buying multiple copies and replacing them as needed. That would probably be cheaper than buying more-elaborate framing. A frame with UV-blocking glass or acrylic would probably slow the damage from light, but would not stop it.