Hi b
I haven't tried them myself but I understand that the nappy insert can help enormously.
The other things to try might be double diapering or plastic pants over the top of the diaper.
Otherwise, you you try a nappy change when your get your DS up for the dreamfeed, before you actually start the feed? It may be that your DS no longer needs a dreamfeed - if he is fully established on 3 meals a day, maybe he doesn't need the extra feed in the night? That might help to eliminate some of the problem.
HTH. Good luck