I have used charcoal in the chip pan of my propane vertical in the summer to smoke cheese. Propane is tooo much heat for my smoker in the summer for cheese. Just a few briquettes was al that was needed in the summer, seem to work well.
I have a cast iron also, although I use a coffee can I was going to try this with the cast iron. I thought some had tried it already, ya'll have tried just about everything we can think of with a smoker. Like you said Debi try and get a little of that charcoal flavor.