I use two piece waterproofs, bought from a camping shop, over fabric kit, and never had any problems. So much quicker and easier to put on and take off than a one-piece. I made my own "crotch strap" from a pair of braces to stop the top lifting.
My mate, Rob Farmer sold it to me ...... he said it was an old aerostich he bought a couple of years ago and was a bit tight for him now .......

Yes I had one too, brilliant, never a single leak. But I don't think they do them any more...Can you still get the old grey/silver Rukka unlined one piece? I had one that lasted me about 15 years and was the best bit of kit I've ever had.