Andy, just a little heads up on polycarbonate glazing. Wise choice not going for corner tabs immediately in the corners. Too much stress there causing splitting due to both X & Y forces. On the other tabs, keep the holes as far away from the glazing edge as possible. Back the polycarb on the tabs with 'cushion' medium density sponge. Use Nylok nuts with the fixings so they are not overtightened, which is another problem that causes cracks. Be prepared on the voyages for some splitting also.