I did some searching first, and i don't doubt it's been requested before. but here it is now.
2 Barrel holding rack that takes 1 tile.
Simple enough functionality. Build the rack: Thinking boards, maybe glue, string and possibly metal nugget (soft probably preferred).
Pick up barrel, right click rack. click the barrel to remove it.
You can't open barrels while in the rack (just like every other container of this kind).
Should be lift able, if empty.
4 Barrel holding rack takes 2x1 tile space.
Boards, wood blocks, leather maybe and probably a hard metal bar, glue, idk what else.
non moveable likely.
-Update 11-29-2016-
Spent the majority of my evening working on this, went to color it in and merge/erase overlap and realized it was portioned way off on the bottom rack. I know a work around but it will take a while to make it look right and I gotta get ready for work in the morning. But I think it's enough to get the general idea

I used a slightly smaller barrel for this (roughly 10% smaller) to keep it somewhat in proportion.
These took longer than i thought to make, but I made these mock ups more as practice and the idea has been in my head for a few couple of days now. Learned a lot. You might notice some improvements between the first normal rack and the double rack.
[edit]
I forgot to mention that this idea is an Either/Or situation. Like if they like the idea of the 4 rack appeals to them they go with that, or the 2 rack. I also didn't have enough time/forgot to make the mock up for the 3 barrel rack (1x2 tiles).
I didn't like the huge attachments at the bottom of the page so I posted the images else where. Let me know if they don't show up in the spoilers.