Same photo but closer view of cleats. Moeller (and I would think other plastic tank mfgrs), specify 3% all around space to allow for tank expansion (not because of heat but because the material absorbs petroleum, from what I gather). The cleats holding these tanks in were butted right up to the tanks, with no expansion space at all, from what I can tell. When the tanks expanded, they pressed on the cover panel - and to some extent the cleat - and "levered" the cleats up out of the sole (they were made of starboard screwed directly into the sole/core). I'm hoping to avoid these issues with the new tanks by installing them differently.

Same photo but closer view of cleats. Moeller (and I would think other plastic tank mfgrs), specify 3% all around space to allow for tank expansion (not because of heat but because the material absorbs petroleum, from what I gather). The cleats holding these tanks in were butted right up to the tanks, with no expansion space at all, from what I can tell. When the tanks expanded, they pressed on the cover panel - and to some extent the cleat - and "levered" the cleats up out of the sole (they were made of starboard screwed directly into the sole/core). I'm hoping to avoid these issues with the new tanks by installing them differently.