A one way midi fuse would direct over-current protection down to the elements, but not the current source. Midi fuses WERE designed as replacements for fusible links, so if you indeed can't get on the road any other way, then a midi fuse would probably be your closest substitute for them. Look at maxi-fuses also.
I actually tried the latter in place of a fusible link 5 years ago, when I had what I thought were circuiting troubles. It turned out, I had a broken motor mount, and when I accelerated, the charging stud from the alternator would ground and short circuit! The fuses blew out TOO fast, even after replacing the motor mount, I found any sudden demand on the charging system had a way of popping maxi-fuses. This is why I took such a vehement tone at first regarding the suggestion from your mates at the auto supply.
Design for worst case scenarios, and upgrade your charging circuit to #8 wire, with 80 amp midi fuses, and you might do well.