Keep my mash warm

[Greenguy]

Hey guys its getting a lil chilly here in New Zealand atm and I am wondering how to keep my mash buckets warm
I have 3 200 litre drums and its around 2-5 degrees C i am thinking about wrapping some hot water cylinder insulation around the outside and then a heavy blanket but don't know if that will be anuff to keep it around 20C
Have thought about a heated blanket but may b a Lil dodgy to have for long periods of time
Only other option is maybe build a box to house them with a small light and some insulation

Cheers guys any info would be much appreciated