Welcome to the forum
Look on line at Home Depot or Lowes or any place like this close to you. I had to replace wall board in my 1990 25ft. Classic due to water damage. I ordered 1/8th paneling from ACE Hardware. It came with the wall paper on it. It was price at something like $45.00 a sheet. I needed five sheets. Do a search for repairs and see what others have used. Keep us posted with your questions. It will be worth the effort.