Trailer side mount work light help.

[Dale99]

I have purchased an enclosed trailer and at times am needing some light on the outside of the trailer. Ive ordered the 12X12 recessed buckets for this. I am wondering if I should be adding extra bracing at the top and bottom of these? Or would screw/pop riveting these to the alumn skin be enough? Or one side on the rib, and rest to the trailer skin?

Attached is a pic of what I'm wanting to do. Random pic found on the net, not my work or trailer.