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What about a truck parts place or truck stop. There are several here locally that sell all kinds of plugs and such for many applications. They are often able to give advice on which products are the most durable.
I too hate the plastic plugs. The female end (on the truck) has a tendancy for the spring loaded door to come un-sprung. I have also drug both kinds of plugs down the road for many miles (literally, the plug came undone and I drug it until it was worn off at a 45° angle) and the metal ones stand up better to that kind of abuse as well.
HA!! Must be that time of year.... The trailer end of mine just cracked where the little screw is holding the end on. Now when I unplug it it is half way apart.