Normally I would agree with that yet he is asking about a setup that is used in literally thousands of various types of trailers successfully everyday.
The voltage drop will reduce as the batteries recharge while travelling. The truck will itself limit the current to ~ 30A. I do not know specifically about the Dodge but I believe 30A is typical for Dodge, Ford, Chev.
It will work for him without altering the system except where he has to go to the boat itself.
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