Thanks both of you! I'm not worried about water resistance. It's either under a cover on a CG pedestal, or the prongs and receptacle are going to get wet in the rain anyway.
Both plugs remind me of what was on our first coach. It got hot one day and I opened it up, tightened the screws, and it was much better. When I got home, I re-did the job, adding those cupped washers that hold the wiring in place on water heater timers, and stainless screws. It was good (no, great!) thereafter.
Chris, I thought it was one of the CAMCO plugs that you recommended awhile ago. If this PI plug is the one you like, that explains why I couldn't find it in CAMCO.
Chasing your leads on Amazon, I found
This Conntek TT-30R that looks pretty good, and the reviews indicate that it CLAMPS the wiring.