I rolled the cylinder in a fairly thick rubber floor mat and then ratchet strapped it with 2 straps to a Black and Decker Workmate portable table. The rubber mat provided extra grip on cylinder to keep it from turning. Also on the Workmate you can open up the center maybe 4 inches where I could nest the tank to further keep it from rolling. Once I got it all tightly strapped in, I used a large crescent wrench, 15 inch I think, and was able to get it on the flat spaces on the tank valve and bust it free. It didn’t take much to come loose.
If you don’t have a workmate table, you might try something like a wood picnic table bench, anything somewhat narrow and sturdy to lay your tank on and get a couple straps around.