I've had Indian Runners manage it all perfectly well on their own. They didn't breed last year, possibly because they are getting a bit older. In previous years when they have it tends to be later on in the Summer, July/ August I suspect if you force the issue earlier on you are more susceptible to humidity problems. They seem to need to feel even more secure than some other birds, consequently have sat right in the middle of a patch of stinging nettles, that sort of thing, rather than a broody box that you may feel is more secure. So good ground cover and set up some potential nesting spots for them rather than assume they will find a corner of the duck house.
I've also had them successfully hatch under a broody hen.