I've got to build a new A Frame and thinking of building it out of Aluminium,

The current frame to 50x50 Gal, probably 1.5-2mm thick. It's lasted 12 years but I figure I better not push my luck and try to get 13 years out of it.

Does anyone have any experience with Aluminium Frames? I know it needs to be thicker (maybe 3-5mm) but what else should I be aware of (coatings etc)

Any advice would be appreciated.