You all are so great!
I was wondering why none had written back then I clicked on my thread to check what I'd written and all this was there.
In the meantime I'd called airstream who were much less helpful, but told me that the originals were made by Kelsey or Casey (?) Hayes whose business was pretty much taken by Dexter.
Now I know what I'm doing. I'm going to go ahead and buy the backing plates from a trailer supplier.
Thanks again to all of you.
I guess I should try to figure out how to update my profile, but I'm writing you from what today was extremely foggy Santa Monica, CA.