Make sure that those heaters won't blow the herpstat...that's 400 watts of power, and I don't know how much power that herpstats are rated for...I know that it isn't very high.
Using an 11" piece of flexwatt in each cooler will be a whole lot more efficient than the aquarium heaters, as well as eliminate the possibility of the water pan drying out and killing the heater. A single piece of flex will have no problem heating that cooler to 88-89 degrees...just my .02
the flexwatt idea sounds pretty good. i think i'll try it out tonight. do you rely on only vermiculite to keep humidity up in a setup like that? i guess the egg box should still be elevated over the heat tape right?