Nice work Mark. I usually boil the bands and put them on the mandrel while they are hot, they stay in place pretty good like that, just did some this morning. Bands are prefitted to the horn before they go in to boil. Once turned they go back in boiling water and when soft onto the horn. Another way is to spray the mandrel with water, push the band on, the wood will swell and hold the band in place.
I'm sure there are other ways but this is what has worked for me for years.
Tim