For the record, keeping a tree alive and getting fruit are two different things. I watched a fully mature soursop that had been planted up against the south side of a building in a large asphalt parking lot just south of Avon Park for a number of years. Other than its remarkably ideal situation, it recieved no other protection. The tree survived in 9b but failed to fruit. By late summer it would have recovered from the cold and would bloom. This did not give the fruit enough time to ripen before winter. Sadly, the tree was cut down 2 years ago, so I can't observe it anymore.
However, durring the warmest year here that I can ever remember (last year) we did harvest a soursop that made it all the way through the winter.