Patio furniture cleaner
The PO of our '66 Tradewind gave us a bottle of Patio Furniture Cleaner. She said it was the best product she had used to clean the inside walls. Now I don't know if the hull liner in yours is made of the same plastic material as ours but I offer the idea. I am not sure who makes the product. I can check tomorrow for you if it sounds like what you can use.
Neil and Lynn Holman
Kirk Creek, Big Sur, Ca. coast.
1966 Trade Wind
1971 Buick Centurion convertible
1969 Oldsmobile Ninety Eight