Twin fin trailer setup:

Twin fins are looser than a thruster and are difficult to control.  Adding vektor fins to the side positions of a twin setup will give the board more stability and drive.  A thruster fin creates drag in the center of the board where water is directed which can slow you down.  By adding two Vektor fins to the side rear positions of the twin fins you add more surface area at the rails.  The added fins work together to create a wider turning radius increasing stability and drive while maintaining speed through the center of the board.