Sounds like 'delamination' its come away from the insulation. Check with manufacturer if that could be the cause.The following is the only details I've got for them.
Buccaneer Caravans
The Airfield
Full Sutton
York
North Yorkshire
YO14 1HS
01759 372325
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix caravans/motorhomes.