how do you stop an air filter from freezing?

I live in Iowa and my work shop doesn't have heat so temps are all over the place. I'm setting up a hypertherm 45 plasma cutter with inline air filter and don't want the moisture collected in the filter to freeze. I'm in and out all day so not practical to move the machine into an insulated space. have thought about wrapping it with heat tape but wonder if anyone has a better idea or can recommend a smaller temperature sensitive heater I could attach to the filter (don't want to use an always-on type) ....any ideas would be appreciated.

update......think I'll try a block heater on it, plugged into a thermostat controlled outlet and see if that works.....better ideas would be appreciated....