The benefit of Dave’s pipe design is that if you are using the tank standing up then there is great tip over protection. If you are using the tank on its side, idoc’s design is also nice particularlywith the straps. All great ideas.
Here's what I did with $15 worth of Velcro, and an old strap and rag I found in the drawer. It makes for easy carrying, yet allows for visual access to pertinent tank data for filling. I put the cloth side of the Velcro against the tank to prevent marring the surface, and the hook side out to provide friction when setting it down. (It's amazing what two cups of espresso will do!):