What a beautiful view from your home!
Storage is always tricky for everyone. The same method doesn't work everywhere, as it depends some on how humid it is and how cool. It has got to be trial and error figuring out what works for you.
It is pretty dry here in the winter, so for me wrapping the tubers in saran wrap works well. After dividing them I dust them with cinnamon for its anti-fungal properties, then wrap up each tuber in saran, pile them in boxes, and store them on the floor of my studio/grow room. My studio is a converted attached garage, so while it is heated, it is a separate heating system from my living space, and in the winter I keep it at 50 degrees, unless I am out there working. The floor is just concrete slab, so that is more like 40 degrees - which is perfect for the tuber storage.
Mary and Arlene have been storing theirs in undivided, unwashed clumps I have heard very good things about that method (the dirt keeps them from drying out) but it takes a lot more space, and I have to many dahlias to try it.
I know quite a few people that store them in vermiculite after dividing.
Ultimately - there are some types of dahlias that store really easily, and others that rot easily, so I think everyone looses some. You mentioned that many of yours come from S.I. and I know they tend to specialize in tubers that are easy to store. - lets face it when you are dealing with the numbers they are, you don't have the time to molly-coddle them.
