The answer to water induced corrosion would be gold plated fuse holders as offered by some marine electrics suppliers. Chances are limited in getting such a fusebox to match OE though.
BTW I had a similar issue to OP on a yacht. The otherwise well respected builder had secured high current 12 volt connections via eye terminals to stainless M10 bolts through a 15mm plywood mounting board. Although the securing nuts were seemingly tight they offered a marginal connection resistance as the wood simply compressed when I tried further tightening. This was only revealed when I burnt fingers on a very hot bolt. I re-engineered with nuts each side of eye terminals so I could really torque up the connections tight. Adding serrated washers helped. Although such a size bolt would have conducted thousands of amps without issue, it was found the eye connection resistance at each end was enough with the currents flowing, to heat the bolt enough to char the wood over time