Australia developed 'pop-top' caravans with good ventilation, ample water storage and high ground clearance. During WW2 RV production was halted in most countries except when required as accommodation for military personnel or essential workers. Between 1945 and 1960, RVs flourished in many western countries as disposable income and leisure time grew. Dedicated RV parks were established to cater to the needs of both short and long-term RV users. Improvements in RV technology including batteries, fridges, gas cookers, toilets and lightweight construction techniques dramatically improved RV comfort levels. More powerful gasoline and diesel engines allowed RVs to increase in size, weight and speed. Regulations were introduced in many countries to control how RVs were manufactured and used. Taking an RV on vacation is today one of the most popular leisure activities in Europe, the US and Australasia and increasing in popularity in countries where space and facilities permit. Industry In the United States, about 85 percent of recreational vehicles sold are manufactured in Indiana, and roughly two-thirds of that production in Elkhart County, which calls itself "the RV Capital of the World", population 206,000. The industry has US$32.4 billion annual economic impact in Indiana, pays US$3.1 billion in taxes to the state and supports 126,140 jobs and US$7.8 billion in wages, according to the RV Industry Association. The recreational vehicle industry around Elkhart is part of a large network of related transport equipment companies, including utility trailer makers and specialty bus manufacturers, who source from the same supply chains. The industry has taken hits from US tariffs on steel and aluminum and other duties on RV parts made in China, from plumbing fixtures to electronic components to vinyl seat covers. Tariff-related price hikes forced manufacturers to pass on some of the increased costs through higher RV prices, which in turn has contributed to slower sales. Shipments of RVs to dealers fell 22% percent in the first five months of 2019, compared to the same period a year earlier, after dropping 4% in 2018. Some trailer companies are using innovative materials in new ways to make trailers lighter, more durable and more cost efficient. Cortes Campers LLC has filed for multiple new patents and have improved manufacturing techniques to address issues such as frequent repairs, supply chain issues, mold, mildew and catastrophic failures of key components of travel trailers. The new double hulled completely redesigned travel trailer is made of fiberglass and