I felt like two full barrels would be too heavy and too tall to be practical, but did extend one by one third a barrel. I cut the top rim off the top of one barrel, then cut another barrel at the first rib leaving a flared bottom end. I heated the 1/3 barrel flared end with a torch to expand the metal as much as possible, then using a section of 4x4 post and sledge on top hammered it down onto the full barrel. I then used construction adhesive around the joint to seal it. The legs are on a cradle that holds the barrel. I remember the tolerance of the cradle was so tight, that the cradle had to be heated with a torch to expand the metal enough to insert the barrel. There is a sheet metal funnel inside the bottom of the feeder with the air space under it filled with an expanding foam and construction adhesive around the edge to seal it further. The legs have axle grease or Vaseline on them in this picture and had to be added regularly to keep the coons off. Not pictured I have been testing on this feeder using a slinky slipped over each leg fastened at the top of the leg to find a way to get away having to maintain the grease on the legs. So far it seems to be working.
This extended barrel has given me 30+ years service.