Have you tried adding more custom barrels from many other mods?
You should try all the barrels from the following mods:
Possessed Props by Weeb_Doomer9997
Nuclear Barrels by ReactorCore
Barrels O' Fun by Pega6us
All those and more mods are available on ModDB if you want to try them, and soon, you'll find more new barrels to add.
My favorite custom barrel is the Happy Barrel from Possessed Props. He's got some cool legs and a really cool smile. You should add him to the next update for Not Enough Barrels, and yes, you can add more new variants based on that guy.