Don't let this happen to you. A few weeks ago I noticed that one of the braces to the lower lip of my passenger side wheel surround panel had come loose just in front of the tire. I made a mental note to re-attach it. However, returning from our next trip from visiting my brother in Florida, it must have been fluttering and worked the screws loose at the front of the panel. I heard a flapping noise, then a bang against the side wall below the passenger window, then nothing. I stopped at the next exit and I found what you see in the attached picture.
After looking long and hard, I was unable to find one in salvage. I had to order one direct from Winnebago. It had to be manufactured and the cost is $731 plus shipping. A factory order was placed and delivery time was quoted as four to five weeks. I should be receiving it soon. The original part was pure white plastic. However they only make the replacement part in black plastic, so I will also have to pay to get it painted.
What to look out for: The framework behind the panel is plastic and steel. Some parts of the frame were fastened with screws, some epoxied, and some were attached by what looks like 3M auto trim tape. The braces on mine are attached by aluminum pop rivets, a very poor choice of fasteners for this application. I am going to replace the driver's side pop rivets with stainless steel screws, and the same on the new panel when I install it.
So, check your panels, look for loose brace attachments and loose screws around the perimeter of the panel. Also, check to see if any portion of the panel has separated from the frame due to failure of the epoxy or trim tape.
To get access to the back of the panel, remove the front and rear screws, and it swings up just like the baggage doors (the panels are attached the same way as the baggage door, on hinges inserted into the lower trim channel).