Use of dielectrics like I suggested is warranted. Yes, it is non conductive. BUT the action of pushing the contacts together will wipe it off that specific area. NO contact has perfect mating, none I've seen. There are air gaps, tiny but present, and the remaining dielectric will fill those gaps slowing air contamination caused corrosion.
It will also slow the wiping or wear of the tin coating on the contacts.
You don't need gobs. I usually work some into a blue Scot shop paper towel and then use that to WIPE the plug contacts. All it takes is a thin smear.
Some like stuff like Boeshield spray since when it dries it leaves a waxy film but again getting wiped from the real contact area and the filling the air gaps.
If you are having problems with more than one cord plug burning then have you contacted the marina to replace the receptacle you plug in to. Once the cord plug burns if you can see ANY darkening on the receptacle then maybe the contacts inside, which you cannot see, have been damaged resulting in a less than good contact. That poor contact will then cause the new plug to fail earlier than it should.
Pulling the plug from the receptacle without shutting off power will, if any load is operating, cause sparking which may burn the contacts, both plug and receptacle. All power should be off before unplugging.