sorry you had bad luck with the marans, i have heard its best to dry incubate or incubate them at low humidity, supposedly the dark outer coating makes them lose moisture slower than other eggs.
That has been my experience with Marans. If I add any water or if the humidity is at 30% or higher I have very bad hatch rates from them. At 20-25% hatch rates significantly improve. I now dry hatch everything.