UGF/heater method

Hi.  I'm new to the web, and have learned alot the last couple months by 
reading the mailing list, FAQs, and other postings.  I'm planning on setting 
up a 30-gallon plant tank........but still haven't decided whether I'm going 
to go with UGF or not (one week - yes, the next week- no).  I've decided 
against heating cables  (too expensive, and I'm not handy with electrical 
components).  I've seen some discussions on the UGF/heater method, but 
couldn't find a description of the set-up.  Could somebody tell me how this 
works, or point me in the right direction?