geckobabies
GeckoBabies.com
That's a great idea with the carbon.
Steve, I don't know what you're using for your incubator, but it could be the case that some older fridge/freezers have a less than friendly plastic or foam insulation that gives off some fumes when heated (by the heat tape). Is there a strong chemical or plastic smell in there?
My converted freezer had a plastic smell to it, and I'm pretty dang anal when it comes to these guys. So just to be sure, I threw an activated carbon filter with 3 pounds of active carbon into my incubator. There is absolutely no smell in there anymore.
http://shop.ebay.com/foothill-carbon-filters/m.html
Hope that helps,
Jon