I've had to use supports twice - both for sliding battery cover replacements.
I just could not get either the auto generated supports or the custom placed ones to work from simplify3d.
In the end I just made my own and incorporated them into the design.

I left a gap the same height as the layer print - 0.2mm. Makes them really easy to remove but effective as supports.
Other than that I just design for things to print without supports - makes life a lot easier.