DRLZ, ditch any locking, latching lids. In texas, those barrels heat up to very high temps in the Summer and when latched lock'd they start to sweat inside causing clogging up, especially if spin casting protein by chance. I use the slip on large metal lids with lips and they ventilate much, much better.
Thanks. I actually have 2 food grade barrels that were the first ones I built with locking lids but the lids didn't have a gasket and have been fine. I built another one last year and it had a bolt style locking ring and a lid with a gasket. Clogged up and molded all the corn in that one. I have since replaced with the galvanized slip over lid on that feeder. Seems to only be an issue when it has a gasket around the lid surface.