I think your build looks great. I found a picture of what I was think for the nest box doors. Where you have overhangs for the roof. I think you could incorporate something like this in you build and make it waterproof. Again, YMMV.
I have a rather heavy egg door that opens the way you show. I ended up adding gas pistons. Still I wish I had done a front door. You could consider a front door. Maybe a sliding door. If the overhang is large enough I think it would be watertight. This type door would also allow easier...