Mel
i find that with DD - the short and long snap in booster (the long one in thirds to the front) and then a BBB booster (the big square type) folded in half before the wool cover, is more than enough. we have done this twice and without the extra booster between nappy and cover twice and neither has wet through to the wool cover

but i also find that DD hardly wets through after 3-4 hrs the long booster if it is doubled at the front. The small booster is always dry during the day. so maybe she isnt a big wetter