Hello Garden Web friends.

In the spring of 2012, I propagated grape vines using the following method.
1. A large Styrofoam cooler with drain holes (Omaha Steak cooler)
2. A Seed Heat Mat (brand unknown - black with light green writing)
3. 50% Perlite - 50% Vermiculite mix.
4. Powdered rooting hormone.
The Styrofoam cooler was plugged in and left on my outside deck.

This method seemed to work quite well in the spring of 2012. Many cuttings of various varieties grew with only about a 30% loss in cuttings (that never rooted).

When I tried the same method in the spring of 2013, the system was a complete failure. I discovered the heat pad had temperatures that were extremely inconsistent with cold, warm and hot zones. my grape cuttings were either too cold or they baked from being too hot. Only a small area within the cooler was a success with growing & rooted cuttings (Niagara grapes). Apparently the temperature was just right in this small zone within my cooler.

I have since thrown out this heat pad. I am preparing for the spring of 2014 and I am looking for a better quality heat mat to use. Once I get a new heat mat, I am thinking of using a layer of small bubble wrap as a buffer between the mat and the growing medium to help equalize any variations in heat.

Does anyone have any recommendations for a quality heat mat with consistent heat throughout?
Or does anyone have any recommendations on how I can tweak my grape propagation system?

Thanks!