Fixing up some heat exchangers, and was wondering if it is a good or bad idea to weld around where the manifold pipes enter and exit the housing or box part of the heat exchanger, where they are crimped around the pipe and have gaps where it would be losing warm air. Would it possibly crack the weld or the pipes because of the difference in thickness between the pipes and the sheet metal and as far as transfer of heat or possibly make for carbon monoxide to get in because of a possibility of cracking the pipes? Please advise.