Have you seen this thread?
http://www.trailmanorowners.com/foru...hlight=valance
I'm planning to do the same. I don't think valances will be so heavy as to pull the aluminum skin, especially if the valance hangs flush to the wall.
When I get around to doing mine, I'll post pictures of how I design the valance. My plan is to use fairly thin solid wood stock. I'm considering using rivets to secure the z-clips to the wall. Screws can pull and work loose, while rivets will clamp on both sides. I will try to use the existing holes for the original window track.
However, I had posted a question in a different thread wondering if some of the newer metal stud finders would work to find the aluminum frame members of the TM. I guess either no one has one, or no one has tried it. My 25 year old stud finder is useless.