I used one of the wrap around heaters on my old GSO 12" (ie one of these
http://www.bintel.com.au/Accessories...oductview.aspx )
Worked fine. Just check with Bintel whether you need the 1.25" or 2". From memory the 2" was OK on my scope and the 1.25" is OK for an 8" scope, but check anyway.
I can pump out a lot of heat. I accidentally put mine on full blast one night and the air current were so bad i couldn't see anything clearly. Usually only ran it at the lowest setting.
The heater controller is fine. I have one and it works OK. Just be aware you will need a 12v power source. I found a battery was best solution as I could mount it on the base of the scope.
I second what Allan said about not heating the primary. If dew is a problem on that (which would be rare, it has never happened to me and Colac can be dew central in winter!) the fan is usually better to create some airflow.
Malcolm
PS. One issue I found with the secondary heater is it is held on with just a rubber band, so you have to regularly check it is not perishing, even the low heat required seemed to cause it to deteriorate, so I changed it every 6 months or so.