What kind of metal work do you have.?When you look at alot of conduit and DOM that have been around for a few yrs, you will see that they start to rust from in inside and at any place where they can trap moisture. Just look at how many lower legs rust out.
Some people use little weep holes to let that water out.
Now a bracket or tab is a good method to mount a light , but claps are just just has good. I know plenty of people that drill them 1/8" weep hole in conduit.
if your riggin is painted, just weld on the tabs or bracket and touch it up. That why black and cammo are easy to repair and add on.