Tom:
I used all Lucas switches and they came with round nuts with two small indentations to facilitate securing them. No hex nuts. Pictures posted on our build log. (Chuck and Ryans RCR Build)
I would secure them with the switch off center about 45 degrees. Once reasonably tight, I turned the switch, not the nut, to the vertical position to snug it down. Then we wired everything. No scratches on the painted aluminum panel!
Using a serrated lock washer on the back may also help secure them.
Got my switches from
Finish Line, www.Cobraaccessories.com Good luck! Chuck