The bulkheads of the buoyancy spaces are quite flimsy though once the foam is set behind them they should be quite firm. However, the foam can exert some pressure when being injected and the battery 'room' must be of the correct size, so a box was made to act as a sort of mold plug until the foam is all done and set. The box is lightly glued wood made so it can (I hope) be broken up in situ and removed through the opening in the foredeck, which is smaller than the box.