I agree with Steve, especially if this is a daily thing that you are dealing with all winter long for a daily regimen. You may however be able to get by with a small, safe space heater in the van that you plug in at night. You won't need much to maintain an environment above freezing, especially if it has a thermostat. Sure it will cost you some electricity, a few pennies a night. But it will be much less than the labor and chemicals you will have to do on a daily basis.
The great thing about a thermostat is that the heater electricity won't cost a dime when the temp never gets to the critical point. However, you will find yourself to have done unneeded chemical anti-freezes on some occasions.
Now, if this is a situation where you are storing the vehicle for a week, or even a week-end, you may want to ditch the heater and go ahead and use the washer fluid, or a glycol antifreeze, as the labor of a once done will outweigh the heater idea.