I'm building an outdoor sensor system (a bunch of sensors and a Raspberry Pi inside a plastic enclosure). A few weeks ago, one of my prototypes got too cold (ambient temperature went below 0deg Celsius). While the sensors can handle sub-zero temperatures for a short time, it does reduce their lifespan, so I want to heat the components up slightly.
I bought a heating pad and have got it working (using one of these as a controller). However, it seems to keep all of its heat within the pad, rather than heating up the air around it. For instance, if I put my hand near the pad (2-3cm above it), I don't feel any heat, but if I touch the pad, it is very hot. My thermometer showed it reached above 50deg Celsius, so I know it's working.
How do I go about distributing this heat towards specific components within my enclosure?
Should I just stick a big heat sink onto it, and then have a fan pointing at the heat sink and facing in the direction of where I want the heat to go? Or is there some more efficient method?