Is that an expandable shower curtain rod at the top? If so, it could have caused the crack due to too much pressure. The bottom crack could be due to over-tightened fasteners. Road vibration could aggravate or even cause the issues as well.
Personally I wouldn't think about changing out or sending out the panels. I'd just stabilize the problem. At the top, and at both ends of the shower rod, I'd add a plastic weight-distributing pad so there's not so much pressure in one spot.
At the bottom, I'd slack off the fasteners, glue and/or seal the crack and reseat the fasteners, but not too tight.
I don't know why Winnebago uses such thin panels. The weight savings can't be that significant.
2002 Itasca Suncruiser 35U