It's likely that you're watering too often. The water IS free to migrate into the soil beneath the containers - yes? Oh wait - I just reread your post. If you have mesh over the holes & there is an air space under the bottom, that could make a significant difference. If you have a soil to soil bridge in your other containers, they will behave like raised beds, as far as water movement is concerned; but if the whisky barrels don't have that bridge and aren't wicked, they'll behave like conventional containers.

Al

I didn't use mesh and I do have an air gap.

If I read your post correctly Al, I will bridge the air gap with soil.

thx

Eric