Mike, you are right on with Macdonald & White paint. Brian Gough, Les Fisher and I have been using it for 20 years. We found a gallon of their WW2 paint and then found out they were still in business all these years later. The price is certainly right but shipping hazardous material is a killer. We are lucky that Les' inlaws live just outside Windsor. I have done experiments on my mail box
and the paint stands up real well in all that weather. After a few years it does fade but so does all enamel. A better paint to use that doesn't fade is the two part epoxy but it is $$$$$$$.
For our purposes where the vehicles don't have long term outside storage this paint is great.
Cheers,
Barry