Our No.2 is mounted to an 8ft TREATED 4×6 2ft in the ground 6ft above making the bell about 7ft high. This is still reachable with a step ladder, yet tall enough the grandkids can only reach the pull chain. Post doesn’t need concrete if good soil compacts solid to steady it, but one or more 40lb bags of quick set concrete as the first backfill would help . Sonotube is a little overkill unless you have loose soil that won’t form a cylindrical hole about 12″ – 16″ diameter. A few big galvanized spikes projecting from the buried section might provide some extra “bite” in the concrete. Tamp down the soil fill around the post, filling a little at a time to make sure its compact using the shovel handle, if that’s all that’s available.
So, all soil if it digs, forms a hole and compacts solid like our gravel does, all concrete and 16″ dia.sonotube if you’re in loose sand or soft soil, or a combo if soil compacts well but you want that extra concrete mass ballast at the bottom to help hold the post steady.