<a href=showthread.php?s=&postid=12292940#post12292940 target=_blank>Originally posted</a> by kcress
It won't need to be able to withstand more than a probably a hundred pounds of tension. That's what steel does best! It could be really small. Perhaps 1/4" at the most. You do need to fix it to brackets on the ends that will distribute the forces to the tank sides. Small angle iron? You will need to protect it well from salt water. Paint or stainless.