I've had a Pelican gun case containing recovery gear on my TJ's roof rack for around twenty years with no problems. Its secured by "U-bolts" around the rack's rails with the nuts on the inside of the case and a padlock to keep anyone from easily opening it. No doubt, the contents could be stolen by someone with a cordless grinder but the same could be said for most everything I have on the rig if the thief is determined.
Meant the nuts on the inside





