I need to ask a question or two. Where do you live? and what are your intentions?
Then a little about insulation. All is does is slow the rate of temperature exchange. It can save you money, by allowing smaller wattage bulbs or actually cause it to get to hot and kill your monitor/s. This can happen when you have a nice set up, with all the right temps, then you have a hot day.
In the past and even now, I do not recomend putting monitors outside. And this is one of those times. There are simply too many problems and very little experience with that.
You do not have a good handle on captive husbandry inside. But you want to put them outside. Well outside has far more problems and some are quick to kill your monitor. If you do not understand what the benefit or use of insulation. Then its possible you should wait until you have a better handle on outside cages.
Consider this, inside, we all have about the same temps to work from(room temperature) Outside, we all have different temps and extremes. Remember when they are inside, if they get out, they are still contained in your house or garage. Please think about how many people come here asking how to find their loose monitor(which is in their house) Well, if they are outside, when they get out, they are GONE. Monitors always get out, think about it. So maybe reconsider putting them outside and do some more research.