Its been broken for awhile. there was corrosion on the broken edges.
On one side of the mount plate is a bolt hole (left side in photo), on the other side is a dimple that fits into a hole in the support frame. If the dimple isn't in the hole, but resting on top of the frame, it could add a small amount bending stress to the mount plate. ????
I did find a part number for a new piece. I'm not sure if it available. I'm still undecided as to replace it, or trust my repair.
This Denso booklet shows parts for almost every Fleetwood manufactured. Look on page #36, item # 3-3.