thanks anyway Damo/flatcat!
and Indiana, it was a good discussion too
and tonguello,
your photos are loud and clear and I have no more doubts nor question for you experts
while the good news is the the gaps are nice and wide enough (well, at least wide enough for rifles while samurai aquebusiers will still have to shoot from the sides/edges
BUT the bad news, (clearly shown on your photos) while they stand well, the 'planks' are too perfect...maybe they are supposed to be real reusable PVC/moulded pallets and not those rough wooden pallets i hoped to use to simulate defences for samurai arquebusiers