Your full size 1971-76 GM convertible car has a drain trough in the back to collect rain water and make sure it drains out of the car properly, if this is not installed or not installed properly the water will collect inside the car and cause rust as well as many other problems. Convertible Specialists makes a reproduction gutter retaining rod out of stainless steel so you never have to worry about it rusting out and breaking, the gutter is also available.