I tried to contain them above ground last season - 1st year plants.
I used 55gal blue drums cut in half, (ended up being just over 2'), and drilled small drain holes in the bottom, and lined the barrel end with weed block before putting the dirt/rhizome in it. I then placed it on the ground directly next to my support system so it could drain normally.
Over the course of the season things went great, had good drainage, etc. When I went to pull the half drums at the end of the season and get them up by the sheltered garage, I couldn't move the barrels. The tap roots(?) or something had penetrated the weed barrier and gone down in at least a good two foot into the ground and were promptly ripped out when I got some help to move the barrels.
I was VERY surprised at the size of the tap root (?) for certain varieties vs others - for example Chinook only had 1, maybe two but they were easily as thick as my thumb. Cascade on the other hand was a disaster with roots out everywhere through the drain holes and they had no interest in going down so much as spreading outward from the barrel.
All said and done, I dug out almost a 5gal bucket full of these roots from under the barrel spots as the last thing I want running down my fence line are six different varieties of hops. I'm sure I didn't get them all, but I'm not overly concerned considering the size of the roots that I couldn't get out (less than an eighth of an inch diameter).
I like the barrel idea because I can move them when it's cold or move them along should I get tired of it. I need to figure out how to deal with the penetration of the weed guard issue.
* I say tap root because I'm not sure what the heck they were - they were definite roots, and didn't look anything like the rhizome that was initially planted.
Garbage can minus bottom is a solid idea, but digging the plant/rhizome out later could be a challenge.
IMO.