Outline traced from Slingshot’s own photos, rocker and thickness from its side view. Straight from the photos it held 21.3 L (+18 %). The side view reads the listed thickness, so the photo’s thickness is kept, with a rounder cross-section than the default (it fills 75 % of its width × thickness box, against 88 %), to hold the listed volume. The cross-section’s shape is assumed, not measured.