Here are some pictures of my valances so far. I'm avoiding particle board, but trying to keep weight down as well. (Considering how heavy particle board is anyway, that's not too difficult).
Frame made from .5" x 1" wood stock.
trim added to frame:
Close up of corner. (a nail just happened to hit another sideways splitting a brace.
I'll varathane, then install with z-clips. This one is the prototype, so hopefully the rest could be made in a day.