Zerostart tank heaters are what Frost Heater uses.
There's a current thread happening at TDI Club about them. Many people are saying to save your time and just buy the kit. I've seen a few new kits advertised for about $75.
Ave you resealed your air flaps in the heater box? My heat starts way sooner and blows way hotter since that was done.
I also have half of my radiator covered in cardboard. In a few weeks, the entire thing will be covered.
-Todd