I've been working with a tiny model too. One of the things that I did, aside from changing the precisions, is to work in a factor that is 1000x the real world size. When I finished all my precise work,I scaled down to the real world size and everything looked just fine. Then I "Saved" and lost a bunch of faces. It appears that SketchUp does a "validity check" on saving and finds all the things that become distorted when you scale down. I just couldn't work as tiny as I needed to no matter what.