I have a 1986 46' Connie which should be the same set-up. On ours we have 2 50 amp inlets on either side. One is 50A/240V and the other is 50A/120V. I have found very few marinas that have the 50A/125V outlet in a power pedestal. On our panel the Power selector switch has SP 1 (240V) and SP 2 (120V). Position 1 had SP 1 & SP 2 so I assume you could use 2 cords if your marina power had the 120V option available.
That being said, I have never used the 120V inlet and have no problem running everything on the boat. If you are using the resistance heaters along with other appliances maybe that could be a high draw. I would think that if you are tripping the main breaker you have another issue assuming you are getting the proper voltage and amps from the pedestal all the way to the main panel.
I have attached a picture of our panel, yours should be similar. (Sorry, just found that a HEIC file is not supported, anyone have a fix for this?)
Hope this helps.