For posterity, I am updating this post in the event it may be helpful to others in the future.

After MUCH diagnostic work, a quality indy shop was able to determine that I simultaneously had failures in the aux water pump AND the heating control valve. Replacing one or the other did not fix the problem (aux water pump caused fuse to blow on start; heating control valve was also sticking and causing fuse to blow subsequently). Both parts were replaced and fuse has not blown in about a month. Will update further if there are any changes.