That Progressive Industries part Chris suggests really looks good. Worth the price premium of not more than about $10 over the Big Box ones.
The plug on our old 1984 coach was decently made till you got to the steel screws and washers on its screw terminals. I don't know what they're called, but there are electrical washers with stamped edges that keep twisted wire from squeezing out from under a screw even with an ordinary washer. I salvaged them from something and had three for the TT-30 plug. With those and stainless screws I was able to get things tightened up to where the plug no longer got hot.
Chris' plug takes care of all that right out of the box.
