I ruined one a few years ago by plugging into a bad receptacle at a campground. Since then, I always use the 50 Amp receptacle with a 50 Amp to 30 Amp adaptor if there is a 50 A socket....much more current capability on the larger 50 A contacts.
Also:
1) Always turn the receptacle breaker off before connecting or disconnecting your cable. If you don't, there will be a damaging arc from the current to both the plug and the receptacle. That's true for any appliance also.... I've seen many people unplug things while they are on - especially vacuum cleaners.
2) Examine your plug contacts frequently...small amounts of corrosion can be sanded out.