The barn basement would be better if I could afford to make a more insulated room inside of it. As it is , just to get maybe one degree of additional protection , I hung across the "ceiling" and made "walls" of some extra wide floating row cover that I had around for garden purposes. That makes a sort of room for the figs ,floor is dirt and the side with no partial soil berm gets all the snow bermed against it with the snow thrower. Last Winter it got down to 20*F , this Winter 26*F , the snow berm making all the difference,I think.
No pictures so far , probably for the best as it is a bit of a mess down there.
Greenhouse frame 30 x 48 stored there (no land to put it on , so sold, to be picked up this Spring) and greenhouse benching , some used for driveway garden.
I think you are correct about the longer days here being helpful in ripening figs. Don't get the heat , but the extra light helps. Last summer was perfect here, warmer than usual , but all my figs were to young to produce.
Hope this season is similar to 2010 here.