If you grab TexTools
TexTools the Iron Tool is a pretty nice flatten+relax function that combines nicely with select planar to help manually unwrap stuff.
Usually I just do a flatten map on the whole thing with a 40-50 degree break, and then just start stitching things together.
The real issue you'll have with a hard-surface unwrap is that you'll want to make each UV island its own smoothing group so you get better edge bleeding and hide seams at your hard edges. This can be done relatively quickly by doing your unwrap, then using Tex-Tools UV->3d function to convert your UVs to an edit poly, which you can use to set your smoothing groups easily, and then use the function again to get your model back with good smoothing groups/UVs.