If it’s crazy, then I’m crazy…I’ve got one pils lagering, another fermenting and I’m about to brew a bock under the same conditions. I’ve been doing it for years with good to great results. We have fairly moderate winters with highs 45-55 and lows 30-45 usually. I put the fermenter in a tu of water and put aquarium heater in the water. I hook the heater to a timer and set it to come on during the coldest parts of the night. With a little tweaking I can maintain a fairly consistent lager fermentation temp.
I live in New Berlin, so I deal with the same weather. I will tell you this. I’m fermenting a munich helles right now in my garage. I use a johnson temp controller attached to a ferm wrap, and put the whole thing in a big styrofoam box. I’m trying to keep it at 50°F. Remember that 60°F day we had a couple weeks ago? My ferm temp got up to almost 55°F for a day and a half.
I’m not saying you can’t ferment in your garage in the spring, but I think it will be hard to keep a consistent temp with the wide temp swings we can see here. I thought I would be fine in the middle of January and still got burned. I’m sure you can do a pretty good job of temp control using water baths and ice bottles etc, it will probably be a lot of work though.
I ferment in a chest freezer in my garage modified for the purpose with an external thermostat for the freezer to kick on when its warmer in the garage and a lightbulb on an internal thermostat (set to kick on when the garage is too cold). However, I lager in the garage all winter after completing primary by simply racking to kegs and leaving them in the garage after topping them off with CO2. It works fine. As spring arrives, then I use a spare refrigerator, so my lager brewing slows to allow for less available space to lager the beer.