PP - maybe get a pair of longies or something that completely go over? I notice that my BB Wool covers don't completely cover my snoozywuns (but they don't leak either until his morning flood and thats after he is out of bed anyways) but the shorties that i have cover the snoozywun and the sandman that I have as well...

Maybe you just need to invest in a pair of those?
I have no other suggestions (other than to go with a snoozywun..lol)