40 is pretty cold for even lager strains of yeast. I would insulate the fermenter as well as possible inside the chest freezer to maintain the beer temps more consistently. Wrap in sleeping bag or something similar.
Bigger question is: if you have a temp regulator on your chest freezer, why not bring it inside? Or at least garage where it might be warmer? Would make a perfect lager.
Primary #1: Border Crossing Vienna II #2: Empty
Secondary #1: Blackberry Rhubarb wine #2: Empty #3: Empty
Kegged: Dusseldorf Altbier II
Bottles: Big 50 Barleywine, Framboise Lambic, Russian Imperial Stout, Barolo Wine, Berry Rhubarb Wine, Black Currant wine
On Deck: BGSA, 2 Hearts IPA, Pumpkin Ale, RIS, Pre-Prohibition Lager