You just have to use 50% more aluminum by volume than you would steel - 3/8" plate instead of 1/4" to achieve roughly the same strength. The total aluminum would still be 25% lighter than a comparable strength steel container. Steel is much more abrasion resistant though and aluminum has low fatigue strength - something to consider if its bobbing in the ocean and on trucks for its 25 year+ lifetime.  Wouldn't have to paint it though!