not sure how big your tire is but aluminum wouldnt be my first choice for that application just because it isnt real happy with "cycling" type loads. even the heavy wall harder stuff will fatigue - crack and fail, which can be rather dangerous in certain situations. its the same reason you dont see any trailer hitches or cages made out of aluminum -
if you want light and strong and you have free material, go 4130 high carb steel (or something in that range) then you can drop your wall thickness and it would weigh less than the aluminum version. that stuff cracks too, yea, but its a dam site tougher than the aluminum.
post a pic when ya do it