My "dry" tongue weight was under 10%. With empty fresh and propane, and full waste tanks, I think I'm right at or maybe still slightly under that and it tows fine still. But.... ORV/NorthWoods designs their trailer to keep mass over the axles, and to tow well under all conditions. "Moment of inertia" is really what matters, and there's a rough a correlation with tongue weight, but trailers with mass closer to the axle can be stable with less tongue weight, which is why boat trailers don't sway even with only 5-7% tongue weight.
When my tailer is fully loaded (38' overall), with full propane and fresh water, it comes out to 15% which is about 1800 pounds of tongue weight, so it's a good thing they didn't move the axles back further than they are.