Looks good!! I do have one suggestion because I used an upside down large dog crate last year as my shelter. I totally surrounded the inside and made a floor with 1 1/2" insulating foam. Measured and cut it and used silicone to glue it all together inside of the shelter. I also used double insulation for the front door and cut a 6" hole for the entrance. It would be a bit more work for you, but the insulation is cheap from the hardward supply stores. You could also stuff much more straw in there when it gets colder. They will just burrow into it, the cats love that to surround themselves in the straw.
I live in the Chicago area and they are predicting this winter to be record breaking in the amount of snow accumulation

..... It is SO hard to care for feral's during the frigid months, meaning, hard on our hearts

. I do worry greatly about them and feel so bad about them when it is so dang cold outside
