12mm should definitely be enough might be worth looking up bolt on recovery points even on eBay and look at the specs 1st and work off them as a basis. I look forward to seeing your brackets then I will have something to copy off :) I was thinking even a H shape on cut from some scrap. That way you have a flange underneath the chassis, one on each side for the bull bar bolts and then you will be left with a piece hanging down to drill holes for recover points. Hard to explain withought a sketch

