A very good solution and something that is almost essential to old truck repair is a flux wirefeed welder. Harbour Freight and others sell these for about $100 operates on 115 ac. A angle grinder is available for about $20. Any one can weld light work with one of these.Works well to add metal to small holes . Grind the excess and you have a good repair. A little practice and your repairs will be long lasting. A trick that a guy told me about is "nozzle dip" available from NAPA. Dip the nozzle into the dip and it helps make good contact and helps the sputter. The fiberglass and other fillers will work better if the metal is replaced rather than filling a hole with resin.
Rember that a bad welder is a good grinder.
