I'd take untamed's advice and go for two or even three smaller Ebo Jagers rather than one big one. On my 150 gallon system I run two 150s and a 250. I'd also try to keep the top of the heater (where the thermostat is) dry and out of the water.
If you really want to be safe, get an external temperature controller which has a much more reliable thermostat and alarms. Here's one example:
http://www.jlaquatics.com/phpstore/s...t_ID=ct-pptemp