I think the jugs are a good start in that case.
The only other non-power technique available is to pile snow over the enclosures,
my stuff that is covered right now is between(various enclosures)29(F) and 33(F)depending on how much snow is covering them 😉
With the exception of my styrofoam covers which are around 20(F)-Outside temp is 12(F)here
<img src="http://weathersticker.wunderground.com/weathersticker/big2_cond/language/www/US/IA/Fairfield.gif" alt="Click for Fairfield, Iowa Forecast" border="0" height="60" width="468" />