Drilled spar mounting holes in mast plate and clecoed mast to spar. Match-drill four #40 holes for skin support, then removed skin and dimpled match-drilled holes. Online research had supplied several different ways to install this type of mast. Van's tech support suggested that having rear support may be a good idea, but suggested using a triangular bracket attached to the adjacent rib. Fabricated a template from card stock to come up with a workable design.