The problem with making the connections inside the box is that now your box is stuck in your yak unless you have some other connector up the line. I would put the fuse inside the Battery box too. I am currently using some inline brake wire connectors outside both my battery boxes. They are made for trailer hookups so they are designed for weather. I think the actual connection might be made of aluminum.
I use dielectric grease in both the female ends and have not had to replace one yet. I cut the loop towards one end and use the long wired side to mount directly through my box (with Goop) through the fuse (on one pole) to the battery. Then I connect apair of inline wire connecting sleeves on the other side and goop the ends after crimping well. Attach the other side of the sleeve to your FF power wires and Goop again.