[image credit Gary]
I attempted to purchase locally but could not find the exact one I wanted, so I got this one on line from Good Ideas, Inc. They are in Lake City, PA, so at least it did not have to travel far to reach me. It's the Rain Wizard 50 (note that I have no financial interest).
The back is flat, and from reader comments the plastic is sturdy enough that this model is not plagued with the complaint that when full of water the weight causes the back to bow out.
The purpose of the base I built from landscape timbers stacked 3 high is simply to raise the barrel enough so that you can easily get a watering can or small bucket under the spigot.
The link to Ultrarunning is admittedly tenuous--it's just that with the advent of an early hot spell here in south-central PA, I am reminded again of the importance of hydration when we run in the backcountry. On a warm day I find I need about a bottle an hour (20 oz or so) and even then I am still drinking the rest of the day to catch up.