Yes,no,maybe so certainly,,,,,,,,,,,depending on a few factors. Trusses desighned to span 30 feet are common but not all 30 foot trusses are desighned for free span. An experienced framing carpenter can judge by other rooms and walls if this is pratical. If you are unable to get eyes on by a pro, you can eliminate any doubt by nailing a sheet of 3/4" plywood to either or both sides of truss(s) MID_POINT between remaing walls.

You could also post a rough sketch of floorplan with measurments to give us better idea of what you are dealing with.

BTW, double top plate is normal whether or not trusses are used.