Instead of learning from your mistakes and using storage blocks made from metal, you could do what I always do and cheese the entire process and not learn a thing.
Blocks don’t burn unless they’re directly exposed to air blocks (unless barrels have special behavior that I’m unaware of), you could use small non-flammable blocks like pebbles or metal fences (i believe GT has ones that would work nicely for this) to cover up the exposed bits of your barrels. If all else fails, have a waterfall in front of the barrels, it’s both safe and aesthetic!