Hi Jason - every closed NURBS surface has a seam so it isn't really something that can be totally avoided.

One thing that can get tricky is when a seam is not quite lined up with edges from adjacent surfaces. It is particularly tricky when they are pretty close to being lined up so that it is hard to notice the small edges.

That's what you've got in this case - it looks like the main issue is that you can't get that one piece filleted?

If you select what looks like the main edges there:



If you zoom into those 2 circled areas above, you can see there is actually a little tiny additional edge in each of those spots:



If you select those 2 little tiny edges in addition to the longer edges, then fillet will work on it, (radius 0.3 here):




There are some things that I should be able to do to improve this in the future, but for the time being when you have a seam like that and you're not getting a proper fillet, zoom in to the seam area to see if there are any small edges in there.

- Michael