Bruce :

Here is a link. I think you can get (look under) a sub. heater and sub. heater module and together they will work as the outside of the module does not get hot. But check on that I am not sure exactly how it works . They also have a controler that has a big temp. range -30 to 100+. Also a lot of other options. It looks like some of the pond heaters would work also.

http://www.aquaticeco.com/index.cfm/fuseaction/listings.subsections/sid/38