The external fuses installed in-line of the main battery cable installation is not there to protect the Converter/Charger unit but to protect the battery cables wiring in case of short circuit at the converter/charger end of the battery cable. Without the in-line fuse close to the battery source could burn down your trailer. Your battery bank will produce a whole bunch of DC CURRENT until the batteries either run down or explode.
I follow these installation techniques around any high current battery cables in both the trailer and truck start battery high current cables distributions.
I have learned along time ago the follow basic installation procedures when working around high current DC cables. It falls under the concept to learn not to burn for me over the years...
Roy Ken