That's called Dutch Roll. The full size V-tail Beechcraft Bonanza has a distinct Dutch Roll in rough air. Usually it means there isn't enough lateral area to damp out the yaw motion. The Bonanza seems to get it from the V tail plan. At least one early Boeing 707 airliner crashed because the captain failed to correct Dutch Roll properly. The 707s got a yaw damper after that. Jets with swept wings have built-in Dutch Roll. Passengers in early 707s spent a lot of time airsick until they put the dampers on all the jets.

The point is that fast, slick planes like the Rocket are more likely to have some Dutch Roll. Trim and alignment can play a roll, but the roll may be built into the design. If the alignment and trim are right, I'd consider taping a temporary ventral fin of stiff cardboard or balsa (to the bottom of the tail cone, underneath) and see if it cures the roll. If I remember the shape of the Rocket tail cone correctly, it could be short on lateral area.