Some years ago I made one out of strapping.
I cut 3 legs and bent them on the bottom as a foot, attaching them to the tongue with bolts. I took another piece of strapping and wrapped it around the tank to get it mould it round and then attached it to the top of the
legs. I had at least 2 to 3 inch excess on the band which was used with a bolt and wing nut to tighten and snug the propane
tank in it's "new holder"
I liked this type of holder because all I had to do was loosening the wing nut and lift the tank out. Since it was so easy to remove I added a chain and a couple of locks so the tank couldn't walk off.