The problem may have originated with the park plug. I have gone into parks where I would hook up to the plug because it was obviously overheated from use by previous users; cracked and blackened. Clean connectors on the male side can't make up for loose/ damaged contacts in the female side.
Edit: OK, a re-read of your post, I miss read and thought your problem was with the connection to the park post; not from your surge protector to your cable.
It is possible to overheat connections without tripping a surge protector, with constant high loads. Air conditioning use along with microwave and other high amp draws can cause these problems, and can be made worse by low park power.
Does your surge protector have a low voltage shut down?
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.