Tip #1
After the welding and grinding is done, fill small imperfections with JB-Weld.  JB-Weld can also be used on inside corners to smooth welds that cannot be easily ground.  After the JB-Weld has had time to cure, it can be sanded just like metal.  The best advantage to using it as a filler is that it can withstand up to 600 degrees and therefore will not be affected by the curing process if you have your parts powder coated.