3003 vs 5052 for Framing C channel

My local shop says they can get 5052 but they have 3003 lying about….



Which one should I go with?



.063 thickness



Thanks



And this is not for a restore or even an airstream but my "airstream-constructed-like canned ham" project.



And I'm doing 1.5 inch on all three legs.



And for the skins I'm using 2024t3 at .036



with hardened universal buck rivets