markbarendt
Member
Mark,
Take a look at the horticultural type warming pads.... low enough wattage... (and an available thermostat you can purchase) that should allow for reasonable temperature maintenance.
<http://www.americanhort.com/root.html#Anchor--Pr-7027>
The thermostats (which one should expect to be 'waterproof' in a horticultural environment) are further down that page...
Ken
Those look interesting, 200 watts seems a bit low for my application though.