I have a 2003 Elkhorn that developed a sagging floor under the mattress in the cab-over area. It seems tight at the side walls but it is noticably by the hampers on either side. One side sags enough so I can stick my finger under the hamper wall. I was thinking of laying 1 1/2" angle iron along both sides of the mattress and through bolting it, probably through some added exterior trim. Does this sound workable? Does anyone have any other ideas?

Sounds like it would work to me. I would try to use alum angle for weight purposes. JMO
Gary