I need to replace the flexible duct from the heater coming onto the cabin area. The one that came with it is a cheap, thin plastic that has torn, i've already taped it once but it keeps tearing, I would like to get something thicker/more durable. I have found some on amazon but am not sure if it will be a perfect fit. Anyone had to replace these? WHere did u buy it?. I don't have my boat with me to look but I would guess the diameter is about 3 inches.