With the exception of constructing a canopy over the nestbox, you have done about all there is to do. We have 100 – 105 degree HI’s here in Virginia but they do not last for long. Nature has a way of cooling itself and you will probably not have any issues with the box. I have thought about using my shepherds’ hooks to hang a piece of plywood in front to the box to shield it from the South-west sun during the day. I am not sure how effective that might be.
David
Stafford, VA