both of mine are made are made of 3/16s plate. i used to have corners made of diamond plate and they held up fine but i dont like how they look.
i have a write up of my rockers in my sig and my corners are in my build. there are quite a few very clean rockers in here (fab forum) and ive seen it done very well with both angle iron and people with a nice big press break. but ive also seen it done not so well. just take your time and dont settle for "well im just not that good at fabricating" bc everyone is capable of doing clean work, the difference is how much time it takes. so biggest suggestion is be patient
and we look forward to the outcome!