BG 3&4 problems

Angeldcf

Our BG Elementals work extremely well, but we have leaks in the back with our BG 3.0s & 4.0s.  I saw that a major difference was the Elementals had the PUL across the interior back.  The OS 3&4s have the cotton up to the seam (hence the leaking when he naps).  They've been washed tons of times.  I've tried folding the back over/inside, but it doesn't stay.  Any tips?

Roxpup

We have flips and they also have the PUL material for the fold over part instead of the cotton (obviously, since they're not pockets).  I'm very used to those and when we got pockets it was an adjustment.  We have a belly sleeper which doesn't really help your question, because we've been having the same problem, but in the front lately.  So I'm curious to see the answers to your post.