Apologies, I'm a EE designer and software guy. We've been CNC'ing prototypes, and my office just bought a very cheap 3D printer.
I'm using Cura as recomended, and wanted to print a piece that has features on both sides.
Here is a screenshot of each side.
So if you laid one side flat, you see how there is a subtractive portion underneath it?
UPDATE I copied some Cura settings from guys and basically tipped this thing to a 45 degree. Here are the results. Pretty good! The finish has some zits and pops, but the surface details are quite accurate enough to fit a PCB board in there with confidence.
I haven't tried printing anything like that, but one trick is to print the piece at an angle of 45°, so as to minimise the number of surfaces that are horizontal (or near horizontal.) You will still need some supports, but far less than if you just plonked it flat on the build plate. My only other recommendation would be to use a slicer that allows you to define custom supports, such as Simplify 3D or CraftWare (but still print the piece at an angle).
You might even be able to print it on a raft/brim with no supports. I've seen other 3D'ers pull this off.