I did this same repair to my 93 880 Lance, amazing I thought just how crappy these campers are built. Plain steel wood screws & staples & chip board they know there building them cheaply!
My steel bumper was rusty also, so I removed it & it was just lagged to the wood stringer that ran under the door & was gone also, because they hadn't sealed where the bumper & fasteners attached to this cross piece.
I recommend removing the bumper & checking this wood. I replaced all mine & replaced it with clear fir.I used 1" marine plywood for both "wings" & used West Epoxy through out the rebuild, so much stronger than any glue or even the wood itself. Besides it penetrates the wood to keep it from rotting in the future.
I used Sikaflex sealant for each screw (SS) then sprayed the inner plywood with a black undercoating to match Lance's "cheesy" black paper material that they had used on mine. I then had the bumper sandblasted & jacks all color matched. It now looks like new but only better by far!
I would strongly recommend using the marine epoxy system over glue, coat all wood with this material (thins out when warm, penetrates better)