Unless Epson totally changed the chemistry of the ink set in the 7800/9900 (which maybe they did), I have to assume that
you are going to experience outgassing. This is going to occur with any RC paper. It will appear over time as a faint fog
on the inside of the glass. I have had outgassing issues with 7600, 7800, 9880 and even the old 1280 (pigment ink).
The problem is that since the back of the paper RC is plastic, the gasses can't pass through the back and are forced to the
front. With fiber based paper, (Epson Exhibition Fiber, or Museo Sliver Rag are examples) you should not have the same
issue.
Paul Caldwell