jkilroy,
The Pflueger Trion 1990 capacity is listed as a DT10 fly line plus 100 yards of 20# backing. You will get additional backing capacity with a WF9 or WF10 line.

If you need still more backing, you could use Scientific Anglers gel spun backing. The 30# gel spun is thinner than the standard 20# dacron.


Tom