Alternate take:  The wiring diagrams are always challenging, but looks to
me like that red wire in the box, and also the feed from the Alternator to
the box, are both 1.5 metric.  So 12 gauge wire would be a decent upgrade.
Why would you need a 10 gauge wire on a circuit with a 7.5 amp fuse?

A simple FLAPS fuse holder should be fine, you don't really need the
weatherproof caps up inside that wiring box, and working space is scarce.
Stuart MacMillan <stuartmacm@gmail.com> "Red wire is 2.5 metric, 10 ga AWG
per Bentley. Best to get a holder with 10 ga pigtails and use appropriate
butt connectors."