I use heat coils I wrap around my carboy(s) when it gets too chilly in the garage, held in place with masking tape... They work pretty good, especially with a blanket put on top of the coils. My wife's electric blanket works nice too (shhhhh).
Yep, I can't afford and don't have room for a fermentation chamber so I hillbilly-rig my beer
I suspect a heat pad would work better than a coil if taped to the side. I'm not sure I'd want to sit a carboy on top and warm up the beer through he dead yeast/trub at the bottom though...
by the way, don't use duct tape to on heating coils. Bad idea.