Your idea has merit! I kept thinking that I would need to have airflow from the forward side of the mounting bulkhead but your way shows that i don't. It'll be tricky to make one but it is worth consideration. Thanks.
I hope it works, because unless someone else disproves it it'll be the first thing I'll try if I go electric! The "ring around the spinner" idea probably can't be beat for efficient cooling, but man I just don't like the looks.