What is the fine-grained topic of the following text: Elkhart, Indiana, USA is known as the "RV Capital of the World" because it is home to many RV manufacturers, including Berkshire Hathaway's Forest River, Dynamax Corporation, Heartland RV, the Damon Corporation, Four Winds International, Hy-Line, Keystone, Monaco, Sun Valley, and Travel Supreme. Only return the topic.
RV manufacturers in Elkhart, Indiana, USA