I agree with all those saying not enough heat tape. The proportional curve doesn't come into play until 1 degree before the set temperature. Anything below a degree on the original Herpstat is full on. So if you have the red led and the temp is a degree below your setting you are getting basically the same amount of power as if the heat tape is plugged directly into the wall (minus a volt or so drop going through the triac). Also I believe alot of the flexwatt failures happen when its run full on for long periods of time. As I recall the manufacture even warns against that and recommend a certain amount of duty cycle. As others were saying its better to have a little extra. Ambient room temp can also play a big part in temperature regulation which is more noticable when the heating device is on the low side for an enclosure. Also fans in a incubator are pretty much mandatory to get good temperature gradiant top to bottom. I also find that not all flexwatt is created equal. There can be decent differences in heating ability between two similiar strips.
Just like your doing, with any enclosure it takes a little experimentation to find the best setup.
Dion Brewington
Owner, Spyder Robotics
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