Frank, looking forward to seeing how you build out your shells! As many bats as you have you are bound to have more than just a few tire kickers living in them;-) Have been meaning to apologize to you for all the mix ups that day. Not only the mis-understanding about the vent slots, but the extra time you had to wait. When you called the first time I assumed you were just leaving your house and I had a good 20 extra minutes. Then I had to rush like mad when I found out you were waiting. My truck was trapped so it ended up being my son being with me instead of my wife...
BTW, the side rails with the long slots can be made with out a router.

I have a router but due to the time involved in setting it up for just a few parts, I have cut all of my long slots (so far) with a table saw. One of my remaining stumbling block on selling completed bat houses is a twin (perhaps even triple) router table built so I knock out side rails quick.
William