Bingo, you might wanna rethink those flaps. I've seen many of those styles where the baleen has shredded but I don't know over how much time - I guess from stopping debris they'll eventually fall off or get cut off.
I used this company (
http://www.duraflap.com/)for my SRW but they do provide dually flaps - these did not require drilling (held on with clips and bolts in case you want to remove them when not needed and they were a good price. You can order them in any length with a custom charge but they were still priced well - I had to have flaps when I towed trailers for a living and they were required to be 4 inches off the ground. You probably don't need anything custom.