[yoko]

Rather than dealing with the additional sealing problems that a heater inside of your canister could create you would be better off to modify a heater into an inline unit. Think of a CO2 reactor with the heater inside.

I agree.

I have thought about DIY a mini canister w/ heater, but figured it was too much trouble/time/money than I have right now.

Here is a link to a DIY inline heater:
http://www.plantedtank.net/forums/diy/36257-diy-external-heater-56k.html?highlight=heater