Hard baseball sized "bump" outside RV

Delamination due to water intrusion will normally, but not always, show up as a soft bubble. Larger areas you might be able to push on it. Also if you tap of the suspected area and compare the sound to known good it will have a hollow sound due to the separation of the fiberglass from the backing board. Considering the Winnebago Intent has a flat rear panel rather than the more common molded rear cap, such as what the front of your coach has, replacing the entire panel is possible. Expensive for labor costs but certainly possible. Stay on top of this with both the dealer and Winnebago.

Fixing delamination isn't difficult. I'm just finishing repairing several square feet in my coach due to a seal failure I didn't catch in time around the stove exhaust fan. Did the repair from the inside.