For those who have later-model coaches with FRP bumpers, the mountings should be checked. Here's what I found on mine:

Front: OK
Rear: I noticed this when I was doing a walkaround, and snagged the left rear bumper, and it flexed! Attached with lag bolts into the wood reinforcement sections in the bumper. These consisted of 2-1/4"x1-1/4" and 2-5/16"x1-1/4" SS lag bolts in each of two rear mounting plates. On the right and left sides (where the bumper curves around the superstructure), 3-1/4"x 1-1/4" sheet metal screws (plain steel, on the right) and one (missing) 1/4"x3" lag bolt (on the left).

The rear bumper's lag bolt fastenings were plagued with dry rot, probably from the road spray infiltration, and only one on the left mounting plate and two on the right, would snug down.

I through drilled one 5/16" hole on each mounting plate, chiseled the opening square with a 1/4" wood chisel, and installed a 4" SS carriage bolt and self-locking nut on each of the two rear mounting plates. I replaced the left missing carriage bolt with a 3" SS one, and drilled out the right to accept 5/16"x3" SS carriage bolt.

"It's always SOMETHING!" - Gilda Radner as Roseanne Rosannadanna, SNL