A 20 long vertical, covering 2 sides? I was thinking 2 16oz cans, and how much black silicone will I need? 1 tube? 2 tubes? Please help. I'm going to home depot tomorrow to get this stuff and all I know is it takes half a tube (5.1 oz) and 1 can for a think layer (covering 2 sides) in a 10 gallon, so I was thinking about twice as much in a 20l vert. So 2 cans (Gaps and cracks?) of Great Stuff and 1 tube (10.2 oz) of GE II 100% Black silicone. Thanks!