Hi Louis!
Bowls take a lot of sanding. I think the best way to sand them is with a spindle sander. Steve has a video where he tours his shop and it show a spindle sander in action. You may already be familiar with them. The round spindles come in various diameters and they go up and down as well as turning. They are a great machine for scrollers, very versatile. It is best to get a spindle sander with a movable base. It allows you to sand at different angles (like most good scrollsaws). Well worth the extra price, if you can swing it.
The other way is good old elbow grease. Sanding by hand is tiring and with bowls it is even worse.
Barry