Stay away from gas heaters.  They exhasut (I believe) water vapor that will screw up your epoxy.  I am sure you will get some other comments that may explain this further.  Making a smaller area is a good idea and then use electric heat (space heaters or lamps)  The fire hazard is a serious concern, especially at night when you are not checking on it.

Paul G

If you go through the Tips for Boatbuilders you'll find good information on heating your work space.  I have also been working on a build in a seperate unheated garage.  I've made a tent using 3 mil plastic drop cloth around bamboo framing, a panel of 1" insulation on a table, and huge recycled blocks of styrofoam covering the ends.  This is kind of my cure box..  I've got four 75 watt work lamps hanging in there, as well as two electric radiant heaters.  I use the heaters to pre-heat the boat before working with epoxy, and it easily gets the space warmer than 70 degrees, the area stays this warm throughout wetout, and then I leave them on a timer of an hour after I'm done the epoxy work.  The area slowly drops to roughly 58 over a couple hours, and then I cycle the heater back on.  Its been working very well for me, altho I plan on making a truely insulated room for my next build. 

Pre-warming the resin and hardener before working with it goes a long way as well.  I store mine in the house (~70 all the time), and then sit them on a little heating pad while I prep the boat and cloth.  Works well enough~

Kiz,

I was concerned about temps getting down into the low 50's and called MAS.  Using the slow hardener they said I was good down to 41 degrees.  Of course, I think Chicago will get colder than that but I was surprised at how low that stuff would go (thermally speaking) and still cure.

I've had no issues glassing and epoxying my hull and deck at around 46-48 degrees (south eastern Virginia).

Larry