I have had a 3-D for 4 years now and have not had any firebox issues. My first thought also was the wood and I see Greg/Dave covered some other topics.. I just use chunk wood from Smokelicious and only use chips (with screen) on my bacon smokes. Not sure if it matters but I do wet the store bought chips before I use them. I have never cleaned my firebox but I replace the alum. foil I put on top after every smoke. Hope I never have this issue but keep us posted on how you resolve the issue..