This is called checking, the fiberglass is what is cracking. Not easily fixable. When Monaco first started having problems with this they did honor warranty claims but as it became worse they quit doing this.
Don't know if it would be covered by an extended service plan or not. Nothing to loose by asking.
My coach has the same thing, use to worry about it and just gave up.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi